https://github.com/aganea created https://github.com/llvm/llvm-project/pull/102681
Before this PR, when using the latest MSVC `Microsoft (R) C/C++ Optimizing Compiler Version 19.40.33813 for x64` one of the Clang unit test used to fail: `CodeGenObjC/gnustep2-direct-method.m`, see full failure log [here](https://github.com/llvm/llvm-project/pull/100517#issuecomment-2266269490). This seems to have been introduced by https://github.com/llvm/llvm-project/commit/c9e5af3944e85c5f1272c48522b4e9eda398b462 however further inspection shows that commit only triggers a bug in the MSVC compiler. It seems that the symptom is bad alignement generated in one of the load instructions: ``` huge alignment values are unsupported %2 = load i64, ptr %1, align 9223372036854775808 ``` When `Builder.CreateLoad` is called [here](https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CGObjCGNU.cpp#L2096), somehow [this call](https://github.com/llvm/llvm-project/blob/main/clang/lib/CodeGen/CGBuilder.h#L110) to `Addr.getAlignment().getAsAlign()` returns a bad alignement. The problem occurs at the highlighted line in the screenshot (`sub bh,cl`):  The code line on the right is translated to the assembly on the right. `llvm::count_zero` returns a proper value (as seen in `rcx`), however `sub bh, cl` uses a bad constant in `bh` (it is not 63 as expected). I think the optimizer meant to use `dil` not `bh`. A few lines below it does `mov byte ptr [rsp + 40h], dil`. If after `sub` is executed I manually set 6 in `rdi`, as it should have been, the test passes. I'll fix a bug with Microsoft will cross post it here. >From 16efda65bb3d30b67b3215d7e8d69a105e2d771c Mon Sep 17 00:00:00 2001 From: Alexandre Ganea <aga...@havenstudios.com> Date: Fri, 9 Aug 2024 16:32:09 -0400 Subject: [PATCH] [Clang][CodeGen] Fix a bad codegen when building Clang with latest MSVC --- clang/lib/CodeGen/CGObjCGNU.cpp | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/clang/lib/CodeGen/CGObjCGNU.cpp b/clang/lib/CodeGen/CGObjCGNU.cpp index 948b10954ebbed..56a3ed1b87b35f 100644 --- a/clang/lib/CodeGen/CGObjCGNU.cpp +++ b/clang/lib/CodeGen/CGObjCGNU.cpp @@ -2092,10 +2092,10 @@ class CGObjCGNUstep2 : public CGObjCGNUstep { auto *classStart = llvm::StructType::get(PtrTy, PtrTy, PtrTy, LongTy, LongTy); auto &astContext = CGM.getContext(); - auto flags = Builder.CreateLoad( - Address{Builder.CreateStructGEP(classStart, selfValue, 4), LongTy, - CharUnits::fromQuantity( - astContext.getTypeAlign(astContext.UnsignedLongTy))}); + llvm::Value *Val = Builder.CreateStructGEP(classStart, selfValue, 4); + auto Align = CharUnits::fromQuantity( + astContext.getTypeAlign(astContext.UnsignedLongTy)); + auto flags = Builder.CreateLoad(Address{Val, LongTy, Align}); auto isInitialized = Builder.CreateAnd(flags, ClassFlags::ClassFlagInitialized); llvm::BasicBlock *notInitializedBlock = _______________________________________________ cfe-commits mailing list cfe-commits@lists.llvm.org https://lists.llvm.org/cgi-bin/mailman/listinfo/cfe-commits
