[llvm] d122d91 - [InstCombine] Fix GEP of GEP fold with opaque pointers

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-12-27T14:56:41+01:00
New Revision: d122d91e37848d47bf0b1851ce0f1793521323cd

URL: https://github.com/llvm/llvm-project/commit/d122d91e37848d47bf0b1851ce0f1793521323cd
DIFF: https://github.com/llvm/llvm-project/commit/d122d91e37848d47bf0b1851ce0f1793521323cd.diff

LOG: [InstCombine] Fix GEP of GEP fold with opaque pointers

We need to check that result and source element types match, as
this is no longer automatically enforced with opaque pointers.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
    llvm/test/Transforms/InstCombine/opaque-ptr.ll

Removed: 
    


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diff  --git a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
index 9bc32e407eee7..aaf07f25e4748 100644
--- a/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstructionCombining.cpp
@@ -1887,8 +1887,11 @@ static Instruction *foldSelectGEP(GetElementPtrInst &GEP,
 Instruction *InstCombinerImpl::visitGEPOfGEP(GetElementPtrInst &GEP,
                                              GEPOperator *Src) {
   // Combine Indices - If the source pointer to this getelementptr instruction
-  // is a getelementptr instruction, combine the indices of the two
-  // getelementptr instructions into a single instruction.
+  // is a getelementptr instruction with matching element type, combine the
+  // indices of the two getelementptr instructions into a single instruction.
+  if (Src->getResultElementType() != GEP.getSourceElementType())
+    return nullptr;
+
   if (!shouldMergeGEPs(*cast<GEPOperator>(&GEP), *Src))
     return nullptr;
 

diff  --git a/llvm/test/Transforms/InstCombine/opaque-ptr.ll b/llvm/test/Transforms/InstCombine/opaque-ptr.ll
index 558aa7c48a383..ab2a109f6103b 100644
--- a/llvm/test/Transforms/InstCombine/opaque-ptr.ll
+++ b/llvm/test/Transforms/InstCombine/opaque-ptr.ll
@@ -161,3 +161,24 @@ define void @varargs_cast_opaque_to_typed(ptr %a) {
   call void (...) @varargs(i8* byval(i8) %b)
   ret void
 }
+
+define ptr @geps_combinable(ptr %a) {
+; CHECK-LABEL: @geps_combinable(
+; CHECK-NEXT:    [[A3:%.*]] = getelementptr { i32, { i32, i32 } }, ptr [[A:%.*]], i64 0, i32 1, i32 1
+; CHECK-NEXT:    ret ptr [[A3]]
+;
+  %a2 = getelementptr { i32, { i32, i32 } }, ptr %a, i32 0, i32 1
+  %a3 = getelementptr { i32, i32 }, ptr %a2, i32 0, i32 1
+  ret ptr %a3
+}
+
+define ptr @geps_not_combinable(ptr %a) {
+; CHECK-LABEL: @geps_not_combinable(
+; CHECK-NEXT:    [[A2:%.*]] = getelementptr { i32, i32 }, ptr [[A:%.*]], i64 0, i32 1
+; CHECK-NEXT:    [[A3:%.*]] = getelementptr { i32, i32 }, ptr [[A2]], i64 0, i32 1
+; CHECK-NEXT:    ret ptr [[A3]]
+;
+  %a2 = getelementptr { i32, i32 }, ptr %a, i32 0, i32 1
+  %a3 = getelementptr { i32, i32 }, ptr %a2, i32 0, i32 1
+  ret ptr %a3
+}