[LICM] Make isGuaranteedToExecute more accurate.
Summary:
Make isGuaranteedToExecute use the
isGuaranteedToTransferExecutionToSuccessor helper, and make that helper
a bit more accurate.
There's a potential performance impact here from assuming that arbitrary
calls might not return. This probably has little impact on loads and
stores to a pointer because most things alias analysis can reason about
are dereferenceable anyway. The other impacts, like less aggressive
hoisting of sdiv by a variable and less aggressive hoisting around
volatile memory operations, are unlikely to matter for real code.
This also impacts SCEV, which uses the same helper. It's a minor
improvement there because we can tell that, for example, memcpy always
returns normally. Strictly speaking, it's also introducing
a bug, but it's not any worse than everywhere else we assume readonly
functions terminate.
Fixes http://llvm.org/PR27857.
Reviewers: hfinkel, reames, chandlerc, sanjoy
Subscribers: broune, llvm-commits
Differential Revision: http://reviews.llvm.org/D21167
llvm-svn: 272489
2016-06-12 05:48:25 +08:00
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; RUN: opt -S -basicaa -licm < %s | FileCheck %s
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2016-07-13 06:37:48 +08:00
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; RUN: opt -aa-pipeline=basic-aa -passes='lcssa,require<aa>,require<targetir>,require<scalar-evolution>,loop(licm)' -S %s | FileCheck %s
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[LICM] Make isGuaranteedToExecute more accurate.
Summary:
Make isGuaranteedToExecute use the
isGuaranteedToTransferExecutionToSuccessor helper, and make that helper
a bit more accurate.
There's a potential performance impact here from assuming that arbitrary
calls might not return. This probably has little impact on loads and
stores to a pointer because most things alias analysis can reason about
are dereferenceable anyway. The other impacts, like less aggressive
hoisting of sdiv by a variable and less aggressive hoisting around
volatile memory operations, are unlikely to matter for real code.
This also impacts SCEV, which uses the same helper. It's a minor
improvement there because we can tell that, for example, memcpy always
returns normally. Strictly speaking, it's also introducing
a bug, but it's not any worse than everywhere else we assume readonly
functions terminate.
Fixes http://llvm.org/PR27857.
Reviewers: hfinkel, reames, chandlerc, sanjoy
Subscribers: broune, llvm-commits
Differential Revision: http://reviews.llvm.org/D21167
llvm-svn: 272489
2016-06-12 05:48:25 +08:00
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target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
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target triple = "x86_64-unknown-linux-gnu"
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declare void @f() nounwind
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; Don't hoist load past nounwind call.
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define i32 @test1(i32* noalias nocapture readonly %a) nounwind uwtable {
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; CHECK-LABEL: @test1(
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entry:
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br label %for.body
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; CHECK: tail call void @f()
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; CHECK-NEXT: load i32
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for.body:
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%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
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%x.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
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tail call void @f() nounwind
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%i1 = load i32, i32* %a, align 4
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%add = add nsw i32 %i1, %x.05
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%inc = add nuw nsw i32 %i.06, 1
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%exitcond = icmp eq i32 %inc, 1000
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br i1 %exitcond, label %for.cond.cleanup, label %for.body
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for.cond.cleanup:
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ret i32 %add
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}
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; Don't hoist division past nounwind call.
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define i32 @test2(i32 %N, i32 %c) nounwind uwtable {
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; CHECK-LABEL: @test2(
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entry:
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%cmp4 = icmp sgt i32 %N, 0
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br i1 %cmp4, label %for.body, label %for.cond.cleanup
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; CHECK: tail call void @f()
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; CHECK-NEXT: sdiv i32
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for.body:
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%i.05 = phi i32 [ %inc, %for.body ], [ 0, %entry ]
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tail call void @f() nounwind
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%div = sdiv i32 5, %c
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%add = add i32 %i.05, 1
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%inc = add i32 %add, %div
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%cmp = icmp slt i32 %inc, %N
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br i1 %cmp, label %for.body, label %for.cond.cleanup
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for.cond.cleanup:
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ret i32 0
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}
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; Don't hoist load past volatile load.
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define i32 @test3(i32* noalias nocapture readonly %a, i32* %v) nounwind uwtable {
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; CHECK-LABEL: @test3(
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entry:
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br label %for.body
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; CHECK: load volatile i32
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; CHECK-NEXT: load i32
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for.body:
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%i.06 = phi i32 [ 0, %entry ], [ %inc, %for.body ]
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%x.05 = phi i32 [ 0, %entry ], [ %add, %for.body ]
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%xxx = load volatile i32, i32* %v, align 4
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%i1 = load i32, i32* %a, align 4
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%add = add nsw i32 %i1, %x.05
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%inc = add nuw nsw i32 %i.06, 1
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%exitcond = icmp eq i32 %inc, 1000
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br i1 %exitcond, label %for.cond.cleanup, label %for.body
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for.cond.cleanup:
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ret i32 %add
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}
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