[llvm] 10aa7ea - [CodeGenPrepare] Freeze condition when transforming select to br
Philip Reames via llvm-commits
llvm-commits at lists.llvm.org
Sun Mar 15 20:15:17 PDT 2020
minor: past tense of freeze is frozen, not freezed.
On 3/14/20 7:10 PM, Juneyoung Lee via llvm-commits wrote:
> Author: Juneyoung Lee
> Date: 2020-03-15T11:10:46+09:00
> New Revision: 10aa7ea951e22dbd7f2ebdeb6410cfbc8a251eb1
>
> URL: https://github.com/llvm/llvm-project/commit/10aa7ea951e22dbd7f2ebdeb6410cfbc8a251eb1
> DIFF: https://github.com/llvm/llvm-project/commit/10aa7ea951e22dbd7f2ebdeb6410cfbc8a251eb1.diff
>
> LOG: [CodeGenPrepare] Freeze condition when transforming select to br
>
> Summary:
> This is a simple fix for CodeGenPrepare that freezes branch condition when transforming select to branch.
> If it is not freezed, instsimplify or the later pipeline can potentially exploit undefined behavior.
>
> The diff shows optimized form becase D75859 and D76048 already made a few changes to CodeGenPrepare for optimizing freeze(cmp).
>
> Reviewers: jdoerfert, spatel, lebedev.ri, efriedma
>
> Reviewed By: lebedev.ri
>
> Subscribers: hiraditya, llvm-commits
>
> Tags: #llvm
>
> Differential Revision: https://reviews.llvm.org/D76179
>
> Added:
>
>
> Modified:
> llvm/lib/CodeGen/CodeGenPrepare.cpp
> llvm/test/CodeGen/ARM/2012-08-30-select.ll
> llvm/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll
> llvm/test/Transforms/CodeGenPrepare/X86/select.ll
>
> Removed:
>
>
>
> ################################################################################
> diff --git a/llvm/lib/CodeGen/CodeGenPrepare.cpp b/llvm/lib/CodeGen/CodeGenPrepare.cpp
> index 373064da7bb8..fd55ef2936b0 100644
> --- a/llvm/lib/CodeGen/CodeGenPrepare.cpp
> +++ b/llvm/lib/CodeGen/CodeGenPrepare.cpp
> @@ -6131,7 +6131,8 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
> // Into:
> // start:
> // %cmp = cmp uge i32 %a, %b
> - // br i1 %cmp, label %select.true, label %select.false
> + // %cmp.frozen = freeze %cmp
> + // br i1 %cmp.frozen, label %select.true, label %select.false
> // select.true:
> // br label %select.end
> // select.false:
> @@ -6139,6 +6140,7 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
> // select.end:
> // %sel = phi i32 [ %c, %select.true ], [ %d, %select.false ]
> //
> + // %cmp should be freezed, otherwise it may introduce undefined behavior.
> // In addition, we may sink instructions that produce %c or %d from
> // the entry block into the destination(s) of the new branch.
> // If the true or false blocks do not contain a sunken instruction, that
> @@ -6217,7 +6219,9 @@ bool CodeGenPrepare::optimizeSelectInst(SelectInst *SI) {
> TT = TrueBlock;
> FT = FalseBlock;
> }
> - IRBuilder<>(SI).CreateCondBr(SI->getCondition(), TT, FT, SI);
> + IRBuilder<> IB(SI);
> + auto CondFr = IB.CreateFreeze(SI->getCondition(), SI->getName() + ".frozen");
> + IB.CreateCondBr(CondFr, TT, FT, SI);
>
> SmallPtrSet<const Instruction *, 2> INS;
> INS.insert(ASI.begin(), ASI.end());
>
> diff --git a/llvm/test/CodeGen/ARM/2012-08-30-select.ll b/llvm/test/CodeGen/ARM/2012-08-30-select.ll
> index 97b732beb4d7..b51688702a54 100644
> --- a/llvm/test/CodeGen/ARM/2012-08-30-select.ll
> +++ b/llvm/test/CodeGen/ARM/2012-08-30-select.ll
> @@ -2,9 +2,9 @@
> ; rdar://12201387
>
> ;CHECK-LABEL: select_s_v_v:
> +;CHECK: vmov.i32
> ;CHECK: vmov
> ;CHECK-NEXT: vmov
> -;CHECK: vmov.i32
> ;CHECK: bx
> define <16 x i8> @select_s_v_v(<16 x i8> %vec, i32 %avail) {
> entry:
>
> diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll b/llvm/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll
> index 05389bfe8d0a..eb4e4ce431af 100644
> --- a/llvm/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll
> +++ b/llvm/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll
> @@ -7,7 +7,8 @@ target triple = "x86_64-unknown-linux-gnu"
> define i1 @PR41004(i32 %x, i32 %y, i32 %t1) {
> ; CHECK-LABEL: @PR41004(
> ; CHECK-NEXT: entry:
> -; CHECK-NEXT: [[T0:%.*]] = icmp eq i32 [[Y:%.*]], 1
> +; CHECK-NEXT: [[MUL_FR:%.*]] = freeze i32 [[Y:%.*]]
> +; CHECK-NEXT: [[T0:%.*]] = icmp eq i32 [[MUL_FR]], 1
> ; CHECK-NEXT: br i1 [[T0]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_END:%.*]]
> ; CHECK: select.true.sink:
> ; CHECK-NEXT: [[REM:%.*]] = srem i32 [[X:%.*]], 2
>
> diff --git a/llvm/test/Transforms/CodeGenPrepare/X86/select.ll b/llvm/test/Transforms/CodeGenPrepare/X86/select.ll
> index 7829376e9db1..390794ab3cda 100644
> --- a/llvm/test/Transforms/CodeGenPrepare/X86/select.ll
> +++ b/llvm/test/Transforms/CodeGenPrepare/X86/select.ll
> @@ -27,7 +27,8 @@ entry:
> define float @fdiv_true_sink(float %a, float %b) {
> ; CHECK-LABEL: @fdiv_true_sink(
> ; CHECK-NEXT: entry:
> -; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[A:%.*]], 1.000000e+00
> +; CHECK-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
> +; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 1.000000e+00
> ; CHECK-NEXT: br i1 [[CMP]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_END:%.*]]
> ; CHECK: select.true.sink:
> ; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[A]], [[B:%.*]]
> @@ -38,7 +39,8 @@ define float @fdiv_true_sink(float %a, float %b) {
> ;
> ; DEBUG-LABEL: @fdiv_true_sink(
> ; DEBUG-NEXT: entry:
> -; DEBUG-NEXT: [[CMP:%.*]] = fcmp ogt float [[A:%.*]], 1.000000e+00
> +; DEBUG-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
> +; DEBUG-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 1.000000e+00, !dbg !24
> ; DEBUG-NEXT: call void @llvm.dbg.value(metadata i1 [[CMP]]
> ; DEBUG-NEXT: br i1 [[CMP]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_END:%.*]], !dbg
> ; DEBUG: select.true.sink:
> @@ -60,7 +62,8 @@ entry:
> define float @fdiv_false_sink(float %a, float %b) {
> ; CHECK-LABEL: @fdiv_false_sink(
> ; CHECK-NEXT: entry:
> -; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[A:%.*]], 3.000000e+00
> +; CHECK-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
> +; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 3.000000e+00
> ; CHECK-NEXT: br i1 [[CMP]], label [[SELECT_END:%.*]], label [[SELECT_FALSE_SINK:%.*]]
> ; CHECK: select.false.sink:
> ; CHECK-NEXT: [[DIV:%.*]] = fdiv float [[A]], [[B:%.*]]
> @@ -71,7 +74,8 @@ define float @fdiv_false_sink(float %a, float %b) {
> ;
> ; DEBUG-LABEL: @fdiv_false_sink(
> ; DEBUG-NEXT: entry:
> -; DEBUG-NEXT: [[CMP:%.*]] = fcmp ogt float [[A:%.*]], 3.000000e+00
> +; DEBUG-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
> +; DEBUG-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 3.000000e+00, !dbg !33
> ; DEBUG-NEXT: call void @llvm.dbg.value(metadata i1 [[CMP]]
> ; DEBUG-NEXT: br i1 [[CMP]], label [[SELECT_END:%.*]], label [[SELECT_FALSE_SINK:%.*]], !dbg
> ; DEBUG: select.false.sink:
> @@ -93,7 +97,8 @@ entry:
> define float @fdiv_both_sink(float %a, float %b) {
> ; CHECK-LABEL: @fdiv_both_sink(
> ; CHECK-NEXT: entry:
> -; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[A:%.*]], 5.000000e+00
> +; CHECK-NEXT: [[SEL_FR:%.*]] = freeze float [[A:%.*]]
> +; CHECK-NEXT: [[CMP:%.*]] = fcmp ogt float [[SEL_FR]], 5.000000e+00
> ; CHECK-NEXT: br i1 [[CMP]], label [[SELECT_TRUE_SINK:%.*]], label [[SELECT_FALSE_SINK:%.*]]
> ; CHECK: select.true.sink:
> ; CHECK-NEXT: [[DIV1:%.*]] = fdiv float [[A]], [[B:%.*]]
>
>
>
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