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llvm-project/llvm/test/Transforms/RewriteStatepointsForGC/codegen-cond.ll

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[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; RUN: opt -rewrite-statepoints-for-gc -S < %s | FileCheck %s
[PM] port Rewrite Statepoints For GC to the new pass manager. Summary: The port is nearly straightforward. The only complication is related to the analyses handling, since one of the analyses used in this module pass is domtree, which is a function analysis. That requires asking for the results of each function and disallows a single interface for run-on-module pass action. Decided to copy-paste the main body of this pass. Most of its code is requesting analyses anyway, so not that much of a copy-paste. The rest of the code movement is to transform all the implementation helper functions like stripNonValidData into non-member statics. Extended all the related LLVM tests with new-pass-manager use. No failures. Reviewers: sanjoy, anna, reames Reviewed By: anna Subscribers: skatkov, llvm-commits Differential Revision: https://reviews.llvm.org/D41162 llvm-svn: 320796
2017-12-15 17:32:11 +08:00
; RUN: opt -passes=rewrite-statepoints-for-gc -S < %s | FileCheck %s
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; A null test of a single value
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
define i1 @test(i8 addrspace(1)* %p, i1 %rare) gc "statepoint-example" {
; CHECK-LABEL: @test
entry:
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
%cond = icmp eq i8 addrspace(1)* %p, null
br i1 %rare, label %safepoint, label %continue, !prof !0
safepoint: ; preds = %entry
call void @safepoint() [ "deopt"() ]
br label %continue
continue: ; preds = %safepoint, %entry
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK-LABEL: continue:
; CHECK: phi
; CHECK-DAG: [ %p.relocated, %safepoint ]
Fix CHECK directives that weren't checking. llvm-svn: 246485
2015-09-01 05:10:35 +08:00
; CHECK-DAG: [ %p, %entry ]
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK: %cond = icmp
; CHECK: br i1 %cond
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
; Comparing two pointers
br i1 %cond, label %taken, label %untaken
taken: ; preds = %continue
ret i1 true
untaken: ; preds = %continue
ret i1 false
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
}
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
define i1 @test2(i8 addrspace(1)* %p, i8 addrspace(1)* %q, i1 %rare) gc "statepoint-example" {
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK-LABEL: @test2
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
entry:
%cond = icmp eq i8 addrspace(1)* %p, %q
br i1 %rare, label %safepoint, label %continue, !prof !0
safepoint: ; preds = %entry
call void @safepoint() [ "deopt"() ]
br label %continue
continue: ; preds = %safepoint, %entry
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK-LABEL: continue:
; CHECK: phi
; CHECK-DAG: [ %q.relocated, %safepoint ]
Fix CHECK directives that weren't checking. llvm-svn: 246485
2015-09-01 05:10:35 +08:00
; CHECK-DAG: [ %q, %entry ]
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK: phi
; CHECK-DAG: [ %p.relocated, %safepoint ]
Fix CHECK directives that weren't checking. llvm-svn: 246485
2015-09-01 05:10:35 +08:00
; CHECK-DAG: [ %p, %entry ]
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK: %cond = icmp
; CHECK: br i1 %cond
; Sanity check that nothing bad happens if already last instruction
; before terminator
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
br i1 %cond, label %taken, label %untaken
taken: ; preds = %continue
ret i1 true
untaken: ; preds = %continue
ret i1 false
}
define i1 @test3(i8 addrspace(1)* %p, i8 addrspace(1)* %q, i1 %rare) gc "statepoint-example" {
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
; CHECK-LABEL: @test3
; CHECK: gc.statepoint
; CHECK: %cond = icmp
; CHECK: br i1 %cond
[RS4GC] Clamp UseDeoptBundles to true and update tests The full diff for the test directory may be hard to read because of the filename clash; so here's all that happened as far as the tests are concerned: ``` cd test/Transforms/RewriteStatepointsForGC git rm *ll git mv deopt-bundles/* ./ rmdir deopt-bundles find . -name '*.ll' | xargs gsed -i 's/-rs4gc-use-deopt-bundles //g' ``` llvm-svn: 259129
2016-01-29 08:28:57 +08:00
entry:
call void @safepoint() [ "deopt"() ]
%cond = icmp eq i8 addrspace(1)* %p, %q
br i1 %cond, label %taken, label %untaken
taken: ; preds = %entry
ret i1 true
untaken: ; preds = %entry
ret i1 false
[RewriteStatepointsForGC] Avoid using unrelocated pointers after safepoints To be clear: this is an *optimization* not a correctness change. CodeGenPrep likes to duplicate icmps feeding branch instructions to take advantage of x86's ability to fuze many comparison/branch patterns into a single micro-op and to reduce the need for materializing i1s into general registers. PlaceSafepoints likes to place safepoint polls right at the end of basic blocks (immediately before terminators) when inserting entry and backedge safepoints. These two heuristics interact in a somewhat unfortunate way where the branch terminating the original block will be controlled by a condition driven by unrelocated pointers. This forces the register allocator to keep both the relocated and unrelocated values of the pointers feeding the icmp alive over the safepoint poll. One simple fix would have been to just adjust PlaceSafepoints to move one back in the basic block, but you can reach similar cases as a result of LICM or other hoisting passes. As a result, doing a post insertion fixup seems to be more robust. I considered doing this in CodeGenPrep itself, but having to update the live sets of already rewritten safepoints gets complicated fast. In particular, you can't just use def/use information because by moving the icmp, we're extending the live range of it's inputs potentially. Instead, this patch teaches RewriteStatepointsForGC to make the required adjustments before making the relocations explicit in the IR. This change really highlights the fact that RSForGC is a CodeGenPrep-like pass which is performing target specific lowering. In the long run, we may even want to combine the two though this would require a lot more smarts to be integrated into RSForGC first. We currently rely on being able to run a set of cleanup passes post rewriting because the IR RSForGC generates is pretty damn ugly. Differential Revision: http://reviews.llvm.org/D11819 llvm-svn: 244821
2015-08-13 06:11:45 +08:00
}
declare void @safepoint()
!0 = !{!"branch_weights", i32 1, i32 10000}