[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 frozen, 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

4 files changed, 19 insertions, 9 deletions

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:%.*]]