[llvm] [InstCombine] Handle constant GEP expr in `SimplifyDemandedUseBits` (PR #116794)

[Yingwei Zheng via llvm-commits]

https://github.com/dtcxzyw created https://github.com/llvm/llvm-project/pull/116794

Closes https://github.com/llvm/llvm-project/issues/116775.


>From 209cc5bf25e513064b25362fe2b3df1b9fb45340 Mon Sep 17 00:00:00 2001
From: Yingwei Zheng <dtcxzyw2333 at gmail.com>
Date: Tue, 19 Nov 2024 20:42:47 +0800
Subject: [PATCH] [InstCombine] Handle constant GEP expr in
 `SimplifyDemandedUseBits`

---
 .../InstCombine/InstCombineSimplifyDemanded.cpp     |  2 +-
 llvm/test/Transforms/InstCombine/ptrmask.ll         | 13 +++++++++++++
 2 files changed, 14 insertions(+), 1 deletion(-)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 5eb807dcb76cef..392c5c78345c29 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -997,7 +997,7 @@ Value *InstCombinerImpl::SimplifyDemandedUseBits(Instruction *I,
             uint64_t MaskedGEPIndex = HighBitsGEPIndex | MaskedLowBitsGEPIndex;
 
             if (MaskedGEPIndex != GEPIndex) {
-              auto *GEP = cast<GetElementPtrInst>(II->getArgOperand(0));
+              auto *GEP = cast<GEPOperator>(II->getArgOperand(0));
               Builder.SetInsertPoint(I);
               Type *GEPIndexType =
                   DL.getIndexType(GEP->getPointerOperand()->getType());
diff --git a/llvm/test/Transforms/InstCombine/ptrmask.ll b/llvm/test/Transforms/InstCombine/ptrmask.ll
index bcbd78e23ed67f..54d1417ff9fd98 100644
--- a/llvm/test/Transforms/InstCombine/ptrmask.ll
+++ b/llvm/test/Transforms/InstCombine/ptrmask.ll
@@ -578,3 +578,16 @@ define ptr @ptrmask_is_useless_fail1(i64 %i, i64 %m) {
   %r = call ptr @llvm.ptrmask.p0.i64(ptr %p0, i64 %m0)
   ret ptr %r
 }
+
+ at GC_arrays = external global { i8, i8, i64 }
+
+define ptr @ptrmask_demandedbits_constantexpr() {
+; CHECK-LABEL: define ptr @ptrmask_demandedbits_constantexpr() {
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[ALIGNED_RESULT:%.*]] = call align 8 ptr @llvm.ptrmask.p0.i64(ptr nonnull @GC_arrays, i64 -8)
+; CHECK-NEXT:    ret ptr [[ALIGNED_RESULT]]
+;
+entry:
+  %aligned_result = call ptr @llvm.ptrmask.p0.i64(ptr getelementptr inbounds (i8, ptr @GC_arrays, i64 1), i64 -8)
+  ret ptr %aligned_result
+}