[instsimplify] Move (extelt (inselt Vec, Value, Index), Index) -> Value from InstCombine

As requested in https://reviews.llvm.org/D135625#3858141

Differential Revision: https://reviews.llvm.org/D136099

diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index fe7b63c..acfac8c 100644 (file)
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -4857,6 +4857,14 @@ static Value *simplifyExtractElementInst(Value *Vec, Value *Idx,
     if (Value *Elt = findScalarElement(Vec, IdxC->getZExtValue()))
       return Elt;
   } else {
+    // extractelt x, (insertelt y, elt, n), n -> elt
+    // If the possibly-variable indices are trivially known to be equal
+    // (because they are the same operand) then use the value that was
+    // inserted directly.
+    auto *IE = dyn_cast<InsertElementInst>(Vec);
+    if (IE && IE->getOperand(2) == Idx)
+      return IE->getOperand(1);
+
     // The index is not relevant if our vector is a splat.
     if (Value *Splat = getSplatValue(Vec))
       return Splat;

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
index 9bb12cb..40acc24 100644 (file)
--- a/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineVectorOps.cpp
@@ -474,11 +474,6 @@ Instruction *InstCombinerImpl::visitExtractElementInst(ExtractElementInst &EI) {
 
   if (auto *I = dyn_cast<Instruction>(SrcVec)) {
     if (auto *IE = dyn_cast<InsertElementInst>(I)) {
-      // If the possibly-variable indices are trivially known to be equal
-      // (because they are the same operand) then use the value that was
-      // inserted directly.
-      if (IE->getOperand(2) == Index)
-        return replaceInstUsesWith(EI, IE->getOperand(1));
       // instsimplify already handled the case where the indices are constants
       // and equal by value, if both are constants, they must not be the same
       // value, extract from the pre-inserted value instead.

diff --git a/llvm/test/Transforms/InstCombine/vector-inseltextelt.ll b/llvm/test/Transforms/InstSimplify/vector-inseltextelt.ll
similarity index 93%
rename from llvm/test/Transforms/InstCombine/vector-inseltextelt.ll
rename to llvm/test/Transforms/InstSimplify/vector-inseltextelt.ll
index b0a6a4e..f716296 100644 (file)
--- a/llvm/test/Transforms/InstCombine/vector-inseltextelt.ll
+++ b/llvm/test/Transforms/InstSimplify/vector-inseltextelt.ll
@@ -1,5 +1,5 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
-; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+; RUN: opt < %s -passes=instsimplify -S | FileCheck %s
 
 ; extracting a just-inserted element should yield the original value
 define float @constant_index(<4 x float> %x, float %val) {