[llvm] deb70a6 - [InstCombine] Don't strip leading zero index for overaligned vector GEP (#184364)

[via llvm-commits]

Author: Nikita Popov
Date: 2026-03-04T08:57:27+01:00
New Revision: deb70a6d643d090c0fcff7be940ce9513c1b5f77

URL: https://github.com/llvm/llvm-project/commit/deb70a6d643d090c0fcff7be940ce9513c1b5f77
DIFF: https://github.com/llvm/llvm-project/commit/deb70a6d643d090c0fcff7be940ce9513c1b5f77.diff

LOG: [InstCombine] Don't strip leading zero index for overaligned vector GEP (#184364)

In this case the stride is not equal to the type alloc size.

Fixes issue reported in:
https://github.com/llvm/llvm-project/pull/180745#discussion_r2860093376

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/getelementptr.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index e5c750fc6b130..94d26705b9045 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -3429,7 +3429,8 @@ Instruction *InstCombinerImpl::visitGetElementPtrInst(GetElementPtrInst &GEP) {
       !FirstIdx->getType()->isVectorTy()) {
     gep_type_iterator GTI = gep_type_begin(GEP);
     ++GTI;
-    if (!GTI.isStruct())
+    if (!GTI.isStruct() && GTI.getSequentialElementStride(DL) ==
+                               DL.getTypeAllocSize(GTI.getIndexedType()))
       return replaceInstUsesWith(GEP, Builder.CreateGEP(GTI.getIndexedType(),
                                                         GEP.getPointerOperand(),
                                                         drop_begin(Indices), "",

diff  --git a/llvm/test/Transforms/InstCombine/getelementptr.ll b/llvm/test/Transforms/InstCombine/getelementptr.ll
index 92b76c5d1b46a..3b062527dbc36 100644
--- a/llvm/test/Transforms/InstCombine/getelementptr.ll
+++ b/llvm/test/Transforms/InstCombine/getelementptr.ll
@@ -123,6 +123,15 @@ define void @test_overaligned_vec(i8 %B) {
   ret void
 }
 
+define ptr @test_overaligned_vec_dyn(ptr %p, i64 %idx) {
+; CHECK-LABEL: @test_overaligned_vec_dyn(
+; CHECK-NEXT:    [[GEP:%.*]] = getelementptr <2 x half>, ptr [[P:%.*]], i64 0, i64 [[IDX:%.*]]
+; CHECK-NEXT:    ret ptr [[GEP]]
+;
+  %gep = getelementptr <2 x half>, ptr %p, i64 0, i64 %idx
+  ret ptr %gep
+}
+
 define ptr @test7(ptr %I, i64 %C, i64 %D) {
 ; CHECK-LABEL: @test7(
 ; CHECK-NEXT:    [[A:%.*]] = getelementptr i32, ptr [[I:%.*]], i64 [[C:%.*]]
@@ -680,7 +689,7 @@ entry:
 define i32 @test28() nounwind  {
 ; CHECK-LABEL: @test28(
 ; CHECK-NEXT:  entry:
-; CHECK-NEXT:    [[ORIENTATIONS:%.*]] = alloca [1 x [1 x %struct.x]], align 8
+; CHECK-NEXT:    [[ORIENTATIONS:%.*]] = alloca [1 x [1 x [[STRUCT_X:%.*]]]], align 8
 ; CHECK-NEXT:    [[T3:%.*]] = call i32 @puts(ptr noundef nonnull dereferenceable(1) @.str) #[[ATTR0]]
 ; CHECK-NEXT:    br label [[BB10:%.*]]
 ; CHECK:       bb10: