[llvm] [InstCombine]Try to fold trunc(shuffle(zext)) to just a shuffle. (PR #78636)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->

@llvm/pr-subscribers-llvm-transforms

Author: Alexey Bataev (alexey-bataev)

<details>
<summary>Changes</summary>

Tries to remove extra trunc/ext instruction for shufflevector
instructions.


---
Full diff: https://github.com/llvm/llvm-project/pull/78636.diff


3 Files Affected:

- (modified) llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp (+10) 
- (modified) llvm/test/Transforms/InstCombine/logical-select-inseltpoison.ll (+2-5) 
- (modified) llvm/test/Transforms/InstCombine/logical-select.ll (+2-5) 


``````````diff
diff --git a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
index 6629ca840a67c0..3470e61cd597f4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCasts.cpp
@@ -103,6 +103,13 @@ Value *InstCombinerImpl::EvaluateInDifferentType(Value *V, Type *Ty,
       }
     }
     break;
+  case Instruction::ShuffleVector: {
+    Value *Op0 = EvaluateInDifferentType(I->getOperand(0), Ty, isSigned);
+    Value *Op1 = EvaluateInDifferentType(I->getOperand(1), Ty, isSigned);
+    Res = new ShuffleVectorInst(Op0, Op1,
+                                cast<ShuffleVectorInst>(I)->getShuffleMask());
+    break;
+  }
   default:
     // TODO: Can handle more cases here.
     llvm_unreachable("Unreachable!");
@@ -363,6 +370,9 @@ static bool canEvaluateTruncated(Value *V, Type *Ty, InstCombinerImpl &IC,
           I->getOpcode() == Instruction::FPToSI);
     return Ty->getScalarSizeInBits() >= MinBitWidth;
   }
+  case Instruction::ShuffleVector:
+    return canEvaluateTruncated(I->getOperand(0), Ty, IC, CxtI) &&
+           canEvaluateTruncated(I->getOperand(1), Ty, IC, CxtI);
   default:
     // TODO: Can handle more cases here.
     break;
diff --git a/llvm/test/Transforms/InstCombine/logical-select-inseltpoison.ll b/llvm/test/Transforms/InstCombine/logical-select-inseltpoison.ll
index 29e2cb42e1bef4..b3d147621b59e5 100644
--- a/llvm/test/Transforms/InstCombine/logical-select-inseltpoison.ll
+++ b/llvm/test/Transforms/InstCombine/logical-select-inseltpoison.ll
@@ -671,11 +671,8 @@ define <4 x i32> @computesignbits_through_shuffles(<4 x float> %x, <4 x float> %
 
 define <4 x i32> @computesignbits_through_two_input_shuffle(<4 x i32> %x, <4 x i32> %y, <4 x i1> %cond1, <4 x i1> %cond2) {
 ; CHECK-LABEL: @computesignbits_through_two_input_shuffle(
-; CHECK-NEXT:    [[SEXT1:%.*]] = sext <4 x i1> [[COND1:%.*]] to <4 x i32>
-; CHECK-NEXT:    [[SEXT2:%.*]] = sext <4 x i1> [[COND2:%.*]] to <4 x i32>
-; CHECK-NEXT:    [[COND:%.*]] = shufflevector <4 x i32> [[SEXT1]], <4 x i32> [[SEXT2]], <4 x i32> <i32 0, i32 2, i32 4, i32 6>
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc <4 x i32> [[COND]] to <4 x i1>
-; CHECK-NEXT:    [[SEL:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[Y:%.*]], <4 x i32> [[X:%.*]]
+; CHECK-NEXT:    [[COND:%.*]] = shufflevector <4 x i1> [[COND1:%.*]], <4 x i1> [[COND2:%.*]], <4 x i32> <i32 0, i32 2, i32 4, i32 6>
+; CHECK-NEXT:    [[SEL:%.*]] = select <4 x i1> [[COND]], <4 x i32> [[Y:%.*]], <4 x i32> [[X:%.*]]
 ; CHECK-NEXT:    ret <4 x i32> [[SEL]]
 ;
   %sext1 = sext <4 x i1> %cond1 to <4 x i32>
diff --git a/llvm/test/Transforms/InstCombine/logical-select.ll b/llvm/test/Transforms/InstCombine/logical-select.ll
index fcca9588767dd9..af1a3e1455e492 100644
--- a/llvm/test/Transforms/InstCombine/logical-select.ll
+++ b/llvm/test/Transforms/InstCombine/logical-select.ll
@@ -707,11 +707,8 @@ define <4 x i32> @computesignbits_through_shuffles(<4 x float> %x, <4 x float> %
 
 define <4 x i32> @computesignbits_through_two_input_shuffle(<4 x i32> %x, <4 x i32> %y, <4 x i1> %cond1, <4 x i1> %cond2) {
 ; CHECK-LABEL: @computesignbits_through_two_input_shuffle(
-; CHECK-NEXT:    [[SEXT1:%.*]] = sext <4 x i1> [[COND1:%.*]] to <4 x i32>
-; CHECK-NEXT:    [[SEXT2:%.*]] = sext <4 x i1> [[COND2:%.*]] to <4 x i32>
-; CHECK-NEXT:    [[COND:%.*]] = shufflevector <4 x i32> [[SEXT1]], <4 x i32> [[SEXT2]], <4 x i32> <i32 0, i32 2, i32 4, i32 6>
-; CHECK-NEXT:    [[TMP1:%.*]] = trunc <4 x i32> [[COND]] to <4 x i1>
-; CHECK-NEXT:    [[SEL:%.*]] = select <4 x i1> [[TMP1]], <4 x i32> [[Y:%.*]], <4 x i32> [[X:%.*]]
+; CHECK-NEXT:    [[COND:%.*]] = shufflevector <4 x i1> [[COND1:%.*]], <4 x i1> [[COND2:%.*]], <4 x i32> <i32 0, i32 2, i32 4, i32 6>
+; CHECK-NEXT:    [[SEL:%.*]] = select <4 x i1> [[COND]], <4 x i32> [[Y:%.*]], <4 x i32> [[X:%.*]]
 ; CHECK-NEXT:    ret <4 x i32> [[SEL]]
 ;
   %sext1 = sext <4 x i1> %cond1 to <4 x i32>

``````````

</details>


https://github.com/llvm/llvm-project/pull/78636