Auto merge of #137271 - nikic:gep-nuw-2, r=scottmcm

Emit getelementptr inbounds nuw for pointer::add()

Lower pointer::add (via intrinsic::offset with unsigned offset) to getelementptr inbounds nuw on LLVM versions that support it. This lets LLVM make use of the pre-condition that the offset addition does not wrap in an unsigned sense. Together with inbounds, this also implies that the offset is non-negative.

Fixes https://github.com/rust-lang/rust/issues/137217.

1 files changed, 18 insertions, 0 deletions

diff --git a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
index b8cef6a7e25..aea2a8dd097 100644
--- a/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
+++ b/compiler/rustc_llvm/llvm-wrapper/RustWrapper.cpp
@@ -1767,6 +1767,24 @@ extern "C" LLVMValueRef LLVMRustBuildMaxNum(LLVMBuilderRef B, LLVMValueRef LHS,
   return wrap(unwrap(B)->CreateMaxNum(unwrap(LHS), unwrap(RHS)));
 }
 
+#if LLVM_VERSION_LT(19, 0)
+enum {
+  LLVMGEPFlagInBounds = (1 << 0),
+  LLVMGEPFlagNUSW = (1 << 1),
+  LLVMGEPFlagNUW = (1 << 2),
+};
+extern "C" LLVMValueRef
+LLVMBuildGEPWithNoWrapFlags(LLVMBuilderRef B, LLVMTypeRef Ty,
+                            LLVMValueRef Pointer, LLVMValueRef *Indices,
+                            unsigned NumIndices, const char *Name,
+                            unsigned NoWrapFlags) {
+  if (NoWrapFlags & LLVMGEPFlagInBounds)
+    return LLVMBuildInBoundsGEP2(B, Ty, Pointer, Indices, NumIndices, Name);
+  else
+    return LLVMBuildGEP2(B, Ty, Pointer, Indices, NumIndices, Name);
+}
+#endif
+
 // Transfers ownership of DiagnosticHandler unique_ptr to the caller.
 extern "C" DiagnosticHandler *
 LLVMRustContextGetDiagnosticHandler(LLVMContextRef C) {