[clang] c048073 - [Clang][CodeGen] Respect -fwrapv-pointer when emitting struct GEPs (#134269)

[via cfe-commits]

Author: Yingwei Zheng
Date: 2025-04-10T00:48:18+08:00
New Revision: c0480738cb3f4b2db47b77f5b18f9819cb995373

URL: https://github.com/llvm/llvm-project/commit/c0480738cb3f4b2db47b77f5b18f9819cb995373
DIFF: https://github.com/llvm/llvm-project/commit/c0480738cb3f4b2db47b77f5b18f9819cb995373.diff

LOG: [Clang][CodeGen] Respect -fwrapv-pointer when emitting struct GEPs (#134269)

This patch turns off inbounds/nuw flags for member accesses when
`-fwrapv-pointer` is set.

Closes https://github.com/llvm/llvm-project/issues/132449.

It is required by https://github.com/llvm/llvm-project/pull/130734.

Added: 
    

Modified: 
    clang/lib/CodeGen/CGExpr.cpp
    clang/test/CodeGen/pointer-overflow.c

Removed: 
    


################################################################################
diff  --git a/clang/lib/CodeGen/CGExpr.cpp b/clang/lib/CodeGen/CGExpr.cpp
index de7c577a23493..451034395976f 100644
--- a/clang/lib/CodeGen/CGExpr.cpp
+++ b/clang/lib/CodeGen/CGExpr.cpp
@@ -4915,6 +4915,9 @@ static Address emitAddrOfFieldStorage(CodeGenFunction &CGF, Address base,
   unsigned idx =
     CGF.CGM.getTypes().getCGRecordLayout(rec).getLLVMFieldNo(field);
 
+  if (CGF.getLangOpts().PointerOverflowDefined)
+    return CGF.Builder.CreateConstGEP2_32(base, 0, idx, field->getName());
+
   return CGF.Builder.CreateStructGEP(base, idx, field->getName());
 }
 
@@ -4972,9 +4975,13 @@ LValue CodeGenFunction::EmitLValueForField(LValue base,
     if (!UseVolatile) {
       if (!IsInPreservedAIRegion &&
           (!getDebugInfo() || !rec->hasAttr<BPFPreserveAccessIndexAttr>())) {
-        if (Idx != 0)
+        if (Idx != 0) {
           // For structs, we GEP to the field that the record layout suggests.
-          Addr = Builder.CreateStructGEP(Addr, Idx, field->getName());
+          if (getLangOpts().PointerOverflowDefined)
+            Addr = Builder.CreateConstGEP2_32(Addr, 0, Idx, field->getName());
+          else
+            Addr = Builder.CreateStructGEP(Addr, Idx, field->getName());
+        }
       } else {
         llvm::DIType *DbgInfo = getDebugInfo()->getOrCreateRecordType(
             getContext().getRecordType(rec), rec->getLocation());

diff  --git a/clang/test/CodeGen/pointer-overflow.c b/clang/test/CodeGen/pointer-overflow.c
index 9c7821b841980..70e3c855bff90 100644
--- a/clang/test/CodeGen/pointer-overflow.c
+++ b/clang/test/CodeGen/pointer-overflow.c
@@ -10,3 +10,24 @@ void test(void) {
   // DEFAULT: getelementptr inbounds nuw i32, ptr
   // FWRAPV-POINTER: getelementptr i32, ptr
 }
+
+struct S {
+  int a;
+  int b;
+  int c: 10;
+  int d: 10;
+};
+
+int test_struct(struct S* s) {
+  // -fwrapv-pointer should turn off inbounds nuw for struct GEP's
+  return s->b;
+  // DEFAULT: getelementptr inbounds nuw %struct.S, ptr
+  // FWRAPV-POINTER: getelementptr %struct.S, ptr
+}
+
+int test_struct_bitfield(struct S* s) {
+  // -fwrapv-pointer should turn off inbounds nuw for struct GEP's
+  return s->d;
+  // DEFAULT: getelementptr inbounds nuw %struct.S, ptr
+  // FWRAPV-POINTER: getelementptr %struct.S, ptr
+}