[llvm] [InstSimplify] Fold (insertelement Splat(C), C, X) -> Splat(C) (PR #102315)
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Wed Aug 7 07:10:27 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms
Author: Benjamin Kramer (d0k)
<details>
<summary>Changes</summary>
The index doesn't matter here.
---
Full diff: https://github.com/llvm/llvm-project/pull/102315.diff
2 Files Affected:
- (modified) llvm/lib/Analysis/InstructionSimplify.cpp (+4)
- (modified) llvm/test/Transforms/InstSimplify/insertelement.ll (+8)
``````````diff
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index 12a3193e63755..c4c174977c475 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -5181,6 +5181,10 @@ Value *llvm::simplifyInsertElementInst(Value *Vec, Value *Val, Value *Idx,
(Q.isUndefValue(Val) && isGuaranteedNotToBePoison(Vec)))
return Vec;
+ // Inserting the splatted value into a constant splat does nothing.
+ if (VecC && ValC && VecC->getSplatValue() == ValC)
+ return Vec;
+
// If we are extracting a value from a vector, then inserting it into the same
// place, that's the input vector:
// insertelt Vec, (extractelt Vec, Idx), Idx --> Vec
diff --git a/llvm/test/Transforms/InstSimplify/insertelement.ll b/llvm/test/Transforms/InstSimplify/insertelement.ll
index 55fab36ddca15..3fe8b8331a40c 100644
--- a/llvm/test/Transforms/InstSimplify/insertelement.ll
+++ b/llvm/test/Transforms/InstSimplify/insertelement.ll
@@ -119,3 +119,11 @@ unreachable_infloop:
%bogus = insertelement <2 x i64> %bogus, i64 undef, i32 1
br label %unreachable_infloop
}
+
+define <4 x i32> @insert_into_splat(i32 %index) {
+; CHECK-LABEL: @insert_into_splat(
+; CHECK-NEXT: ret <4 x i32> <i32 3, i32 3, i32 3, i32 3>
+;
+ %I = insertelement <4 x i32> <i32 3, i32 3, i32 3, i32 3>, i32 3, i32 %index
+ ret <4 x i32> %I
+}
``````````
</details>
https://github.com/llvm/llvm-project/pull/102315
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