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llvm-project/llvm/test/Transforms/SimplifyCFG/switch-dead-default.ll

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[SimplifyCFG] Prune code from a provably unreachable switch default As Sanjoy pointed out over in http://reviews.llvm.org/D11819, a switch on an icmp should always be able to become a branch instruction. This patch generalizes that notion slightly to prove that the default case of a switch is unreachable if the cases completely cover all possible bit patterns in the condition. Once that's done, the switch to branch conversion kicks in just fine. Note: Duplicate case values are disallowed by the LangRef and verifier. Differential Revision: http://reviews.llvm.org/D11995 llvm-svn: 246125
2015-08-27 07:56:46 +08:00
; RUN: opt %s -S -simplifycfg | FileCheck %s
declare void @foo(i32)
define void @test(i1 %a) {
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
; CHECK-LABEL: @test
[SimplifyCFG] Prune code from a provably unreachable switch default As Sanjoy pointed out over in http://reviews.llvm.org/D11819, a switch on an icmp should always be able to become a branch instruction. This patch generalizes that notion slightly to prove that the default case of a switch is unreachable if the cases completely cover all possible bit patterns in the condition. Once that's done, the switch to branch conversion kicks in just fine. Note: Duplicate case values are disallowed by the LangRef and verifier. Differential Revision: http://reviews.llvm.org/D11995 llvm-svn: 246125
2015-08-27 07:56:46 +08:00
; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false
switch i1 %a, label %default [i1 1, label %true
i1 0, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
define void @test2(i2 %a) {
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
; CHECK-LABEL: @test2
[SimplifyCFG] Prune code from a provably unreachable switch default As Sanjoy pointed out over in http://reviews.llvm.org/D11819, a switch on an icmp should always be able to become a branch instruction. This patch generalizes that notion slightly to prove that the default case of a switch is unreachable if the cases completely cover all possible bit patterns in the condition. Once that's done, the switch to branch conversion kicks in just fine. Note: Duplicate case values are disallowed by the LangRef and verifier. Differential Revision: http://reviews.llvm.org/D11995 llvm-svn: 246125
2015-08-27 07:56:46 +08:00
switch i2 %a, label %default [i2 0, label %case0
i2 1, label %case1
i2 2, label %case2
i2 3, label %case3]
case0:
call void @foo(i32 0)
ret void
case1:
call void @foo(i32 1)
ret void
case2:
call void @foo(i32 2)
ret void
case3:
call void @foo(i32 3)
ret void
default:
; CHECK-LABEL: default1:
; CHECK-NEXT: unreachable
call void @foo(i32 4)
ret void
}
; This one is a negative test - we know the value of the default,
; but that's about it
define void @test3(i2 %a) {
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
; CHECK-LABEL: @test3
[SimplifyCFG] Prune code from a provably unreachable switch default As Sanjoy pointed out over in http://reviews.llvm.org/D11819, a switch on an icmp should always be able to become a branch instruction. This patch generalizes that notion slightly to prove that the default case of a switch is unreachable if the cases completely cover all possible bit patterns in the condition. Once that's done, the switch to branch conversion kicks in just fine. Note: Duplicate case values are disallowed by the LangRef and verifier. Differential Revision: http://reviews.llvm.org/D11995 llvm-svn: 246125
2015-08-27 07:56:46 +08:00
switch i2 %a, label %default [i2 0, label %case0
i2 1, label %case1
i2 2, label %case2]
case0:
call void @foo(i32 0)
ret void
case1:
call void @foo(i32 1)
ret void
case2:
call void @foo(i32 2)
ret void
default:
; CHECK-LABEL: default:
; CHECK-NEXT: call void @foo
call void @foo(i32 0)
ret void
}
; Negative test - check for possible overflow when computing
; number of possible cases.
define void @test4(i128 %a) {
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
; CHECK-LABEL: @test4
[SimplifyCFG] Prune code from a provably unreachable switch default As Sanjoy pointed out over in http://reviews.llvm.org/D11819, a switch on an icmp should always be able to become a branch instruction. This patch generalizes that notion slightly to prove that the default case of a switch is unreachable if the cases completely cover all possible bit patterns in the condition. Once that's done, the switch to branch conversion kicks in just fine. Note: Duplicate case values are disallowed by the LangRef and verifier. Differential Revision: http://reviews.llvm.org/D11995 llvm-svn: 246125
2015-08-27 07:56:46 +08:00
switch i128 %a, label %default [i128 0, label %case0
i128 1, label %case1]
case0:
call void @foo(i32 0)
ret void
case1:
call void @foo(i32 1)
ret void
default:
; CHECK-LABEL: default:
; CHECK-NEXT: call void @foo
call void @foo(i32 0)
ret void
}
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
; All but one bit known zero
define void @test5(i8 %a) {
; CHECK-LABEL: @test5
; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false
%cmp = icmp ult i8 %a, 2
Revert @llvm.assume with operator bundles (r289755-r289757) This creates non-linear behavior in the inliner (see more details in r289755's commit thread). llvm-svn: 290086
2016-12-19 16:22:17 +08:00
call void @llvm.assume(i1 %cmp)
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
switch i8 %a, label %default [i8 1, label %true
i8 0, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
;; All but one bit known one
define void @test6(i8 %a) {
; CHECK-LABEL: @test6
; CHECK: @llvm.assume
; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false
%and = and i8 %a, 254
%cmp = icmp eq i8 %and, 254
Revert @llvm.assume with operator bundles (r289755-r289757) This creates non-linear behavior in the inliner (see more details in r289755's commit thread). llvm-svn: 290086
2016-12-19 16:22:17 +08:00
call void @llvm.assume(i1 %cmp)
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
switch i8 %a, label %default [i8 255, label %true
i8 254, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
; Check that we can eliminate both dead cases and dead defaults
; within a single run of simplify-cfg
define void @test7(i8 %a) {
; CHECK-LABEL: @test7
; CHECK: @llvm.assume
; CHECK: br i1 [[IGNORE:%.*]], label %true, label %false
%and = and i8 %a, 254
%cmp = icmp eq i8 %and, 254
Revert @llvm.assume with operator bundles (r289755-r289757) This creates non-linear behavior in the inliner (see more details in r289755's commit thread). llvm-svn: 290086
2016-12-19 16:22:17 +08:00
call void @llvm.assume(i1 %cmp)
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
switch i8 %a, label %default [i8 255, label %true
i8 254, label %false
i8 0, label %also_dead]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
also_dead:
call void @foo(i32 5)
ret void
default:
call void @foo(i32 2)
ret void
}
;; All but one bit known undef
;; Note: This is currently testing an optimization which doesn't trigger. The
;; case this is protecting against is that a bit could be assumed both zero
;; *or* one given we know it's undef. ValueTracking doesn't do this today,
;; but it doesn't hurt to confirm.
define void @test8(i8 %a) {
; CHECK-LABEL: @test8(
; CHECK: switch i8
%and = and i8 %a, 254
%cmp = icmp eq i8 %and, undef
Revert @llvm.assume with operator bundles (r289755-r289757) This creates non-linear behavior in the inliner (see more details in r289755's commit thread). llvm-svn: 290086
2016-12-19 16:22:17 +08:00
call void @llvm.assume(i1 %cmp)
[SimplifyCFG] Use known bits to eliminate dead switch defaults This is a follow up to http://reviews.llvm.org/D11995 implementing the suggestion by Hans. If we know some of the bits of the value being switched on, we know that the maximum number of unique cases covers the unknown bits. This allows to eliminate switch defaults for large integers (i32) when most bits in the value are known. Note that I had to make the transform contingent on not having any dead cases. This is conservatively correct with the old code, but required for the new code since we might have a dead case which varies one of the known bits. Counting that towards our number of covering cases would be bad. If we do have dead cases, we'll eliminate them first, then revisit the possibly dead default. Differential Revision: http://reviews.llvm.org/D12497 llvm-svn: 247309
2015-09-11 01:44:47 +08:00
switch i8 %a, label %default [i8 255, label %true
i8 254, label %false]
true:
call void @foo(i32 1)
ret void
false:
call void @foo(i32 3)
ret void
default:
call void @foo(i32 2)
ret void
}
declare void @llvm.assume(i1)