[InstCombine] Don't fold freeze poison when it's used in shufflevector

With this patch freeze undef/poison will no longer be folded into a constant if it's used as a
vector operand in a shufflevector.

Differential Revision: https://reviews.llvm.org/D143593

diff --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 2679e0a..2621a83 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3959,6 +3959,17 @@ bool InstCombinerImpl::freezeOtherUses(FreezeInst &FI) {
   return Changed;
 }
 
+// Check if any direct or bitcast user of this value is a shuffle instruction.
+static bool isUsedWithinShuffleVector(Value *V) {
+  for (auto *U : V->users()) {
+    if (isa<ShuffleVectorInst>(U))
+      return true;
+    else if (match(U, m_BitCast(m_Specific(V))) && isUsedWithinShuffleVector(U))
+      return true;
+  }
+  return false;
+}
+
 Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
   Value *Op0 = I.getOperand(0);
 
@@ -4008,8 +4019,14 @@ Instruction *InstCombinerImpl::visitFreeze(FreezeInst &I) {
     return BestValue;
   };
 
-  if (match(Op0, m_Undef()))
+  if (match(Op0, m_Undef())) {
+    // Don't fold freeze(undef/poison) if it's used as a vector operand in
+    // a shuffle. This may improve codegen for shuffles that allow
+    // unspecified inputs.
+    if (isUsedWithinShuffleVector(&I))
+      return nullptr;
     return replaceInstUsesWith(I, getUndefReplacement(I.getType()));
+  }
 
   Constant *C;
   if (match(Op0, m_Constant(C)) && C->containsUndefOrPoisonElement()) {

diff --git a/llvm/test/Transforms/InstCombine/shufflevector_freezepoison.ll b/llvm/test/Transforms/InstCombine/shufflevector_freezepoison.ll
index 6a8a88e..9b7dc4b 100644 (file)
--- a/llvm/test/Transforms/InstCombine/shufflevector_freezepoison.ll
+++ b/llvm/test/Transforms/InstCombine/shufflevector_freezepoison.ll
@@ -4,7 +4,8 @@
 
 define <4 x double> @shuffle_op0_freeze_poison(<2 x double> %a) {
 ; CHECK-LABEL: @shuffle_op0_freeze_poison(
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> zeroinitializer, <2 x double> [[A:%.*]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> poison
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[B]], <2 x double> [[A:%.*]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
 ;
   %b = freeze <2 x double> poison
@@ -14,7 +15,8 @@ define <4 x double> @shuffle_op0_freeze_poison(<2 x double> %a) {
 
 define <4 x double> @shuffle_op1_freeze_poison(<2 x double> %a) {
 ; CHECK-LABEL: @shuffle_op1_freeze_poison(
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> poison
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> [[B]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
 ;
   %b = freeze <2 x double> poison
@@ -24,8 +26,9 @@ define <4 x double> @shuffle_op1_freeze_poison(<2 x double> %a) {
 
 define <4 x double> @shuffle_op0_freeze_poison_use(<2 x double> %a) {
 ; CHECK-LABEL: @shuffle_op0_freeze_poison_use(
-; CHECK-NEXT:    call void @use(<2 x double> zeroinitializer)
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> zeroinitializer, <2 x double> [[A:%.*]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> poison
+; CHECK-NEXT:    call void @use(<2 x double> [[B]])
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[B]], <2 x double> [[A:%.*]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
 ;
   %b = freeze <2 x double> poison
@@ -36,8 +39,9 @@ define <4 x double> @shuffle_op0_freeze_poison_use(<2 x double> %a) {
 
 define <4 x double> @shuffle_op1_freeze_poison_use(<2 x double> %a) {
 ; CHECK-LABEL: @shuffle_op1_freeze_poison_use(
-; CHECK-NEXT:    call void @use(<2 x double> zeroinitializer)
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> poison
+; CHECK-NEXT:    call void @use(<2 x double> [[B]])
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> [[B]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
 ;
   %b = freeze <2 x double> poison
@@ -48,8 +52,9 @@ define <4 x double> @shuffle_op1_freeze_poison_use(<2 x double> %a) {
 
 define <4 x double> @shuffle_op0_freeze_undef(<2 x double> %a) {
 ; CHECK-LABEL: @shuffle_op0_freeze_undef(
-; CHECK-NEXT:    call void @use(<2 x double> zeroinitializer)
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> zeroinitializer, <2 x double> [[A:%.*]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> undef
+; CHECK-NEXT:    call void @use(<2 x double> [[B]])
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[B]], <2 x double> [[A:%.*]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
 ;
   %b = freeze <2 x double> undef
@@ -60,8 +65,9 @@ define <4 x double> @shuffle_op0_freeze_undef(<2 x double> %a) {
 
 define <4 x double> @shuffle_op1_freeze_undef(<2 x double> %a) {
 ; CHECK-LABEL: @shuffle_op1_freeze_undef(
-; CHECK-NEXT:    call void @use(<2 x double> zeroinitializer)
-; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> zeroinitializer, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    [[B:%.*]] = freeze <2 x double> undef
+; CHECK-NEXT:    call void @use(<2 x double> [[B]])
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> [[B]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
 ; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
 ;
   %b = freeze <2 x double> undef
@@ -70,5 +76,34 @@ define <4 x double> @shuffle_op1_freeze_undef(<2 x double> %a) {
   ret <4 x double> %shuffle
 }
 
+define <4 x double> @shuffle_bc1(<2 x double>  %a)  {
+; CHECK-LABEL: @shuffle_bc1(
+; CHECK-NEXT:    [[B:%.*]] = freeze <4 x float> poison
+; CHECK-NEXT:    [[B1:%.*]] = bitcast <4 x float> [[B]] to <2 x double>
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <2 x double> [[A:%.*]], <2 x double> [[B1]], <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+; CHECK-NEXT:    ret <4 x double> [[SHUFFLE]]
+;
+  %b = freeze <4 x float> poison
+  %b1 = bitcast <4 x float> %b to <2 x double>
+  %shuffle = shufflevector <2 x double> %a, <2 x double> %b1, <4 x i32> <i32 0, i32 1, i32 2, i32 3>
+  ret <4 x double> %shuffle
+}
+
+define <8 x float> @shuffle_bc2(<4 x float>  %a)  {
+; CHECK-LABEL: @shuffle_bc2(
+; CHECK-NEXT:    [[B:%.*]] = freeze <4 x float> poison
+; CHECK-NEXT:    [[B1:%.*]] = bitcast <4 x float> [[B]] to <2 x double>
+; CHECK-NEXT:    call void @use(<2 x double> [[B1]])
+; CHECK-NEXT:    [[SHUFFLE:%.*]] = shufflevector <4 x float> [[A:%.*]], <4 x float> [[B]], <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+; CHECK-NEXT:    ret <8 x float> [[SHUFFLE]]
+;
+  %b = freeze <4 x float> poison
+  %b1 = bitcast <4 x float> %b to <2 x double>
+  call void @use(<2 x double> %b1)
+  %b2 = bitcast <2 x double> %b1 to <4 x float>
+  %shuffle = shufflevector <4 x float> %a, <4 x float> %b2, <8 x i32> <i32 0, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7>
+  ret <8 x float> %shuffle
+}
+
 declare void @use(<2 x double>)