[llvm] GlobalISel: Fix defined register of invariant.start (PR #125664)
Robert Imschweiler via llvm-commits
llvm-commits at lists.llvm.org
Tue Feb 4 02:25:19 PST 2025
https://github.com/ro-i created https://github.com/llvm/llvm-project/pull/125664
In contrast to SelectionDAG, GlobalISel created a new virtual register for the return value of invariant.start, leaving subsequent users of the invariant.start value with an undefined reference.
A minimal example:
```
%tmp = alloca i32, align 4, addrspace(5)
%tmpI = call ptr @llvm.invariant.start.p5(i64 4, ptr addrspace(5) %tmp) #3
call void @llvm.invariant.end.p5(ptr %tmpI, i64 4, ptr addrspace(5) %tmp) #3
store i32 %i, ptr %tmpI, align 4
```
Although the return value of invariant.start might not be intended for any use beyond invariant.end (the fuzzer might not have created a sensible situation here), an implicit definition of the corresponding virtual register avoids a segfault in the target instruction selector later.
This LLVM defect was identified via the AMD Fuzzing project.
>From 839080f126c645cdf91eaa624359bd04e16cc569 Mon Sep 17 00:00:00 2001
From: Robert Imschweiler <robert.imschweiler at amd.com>
Date: Tue, 4 Feb 2025 03:48:19 -0600
Subject: [PATCH] GlobalISel: Fix defined register of invariant.start
In contrast to SelectionDAG, GlobalISel created a new virtual register for the return value of invariant.start, leaving subsequent users of the invariant.start value with an undefined reference.
A minimal example:
```
%tmp = alloca i32, align 4, addrspace(5)
%tmpI = call ptr @llvm.invariant.start.p5(i64 4, ptr addrspace(5) %tmp) #3
call void @llvm.invariant.end.p5(ptr %tmpI, i64 4, ptr addrspace(5) %tmp) #3
store i32 %i, ptr %tmpI, align 4
```
Although the return value of invariant.start might not be intended for any use beyond invariant.end, an implicit definition of the corresponding virtual register avoids a segfault in the target instruction selector later.
---
llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp | 4 +-
.../AArch64/GlobalISel/arm64-irtranslator.ll | 2 +-
.../promote-dependency-on-invariant-result.ll | 37 +++++++++++++++++++
3 files changed, 39 insertions(+), 4 deletions(-)
create mode 100644 llvm/test/CodeGen/AMDGPU/GlobalISel/promote-dependency-on-invariant-result.ll
diff --git a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
index 3e43299bb81102e..362d856e76a8aa7 100644
--- a/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
+++ b/llvm/lib/CodeGen/GlobalISel/IRTranslator.cpp
@@ -2441,9 +2441,7 @@ bool IRTranslator::translateKnownIntrinsic(const CallInst &CI, Intrinsic::ID ID,
return true;
}
case Intrinsic::invariant_start: {
- LLT PtrTy = getLLTForType(*CI.getArgOperand(0)->getType(), *DL);
- Register Undef = MRI->createGenericVirtualRegister(PtrTy);
- MIRBuilder.buildUndef(Undef);
+ MIRBuilder.buildUndef(getOrCreateVReg(CI));
return true;
}
case Intrinsic::invariant_end:
diff --git a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
index 7a67cf3fd4c942b..15ee5e48a88e6e9 100644
--- a/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
+++ b/llvm/test/CodeGen/AArch64/GlobalISel/arm64-irtranslator.ll
@@ -2262,7 +2262,7 @@ declare ptr @llvm.invariant.start.p0(i64, ptr nocapture) readonly nounwind
declare void @llvm.invariant.end.p0(ptr, i64, ptr nocapture) nounwind
define void @test_invariant_intrin() {
; CHECK-LABEL: name: test_invariant_intrin
-; CHECK: %{{[0-9]+}}:_(s64) = G_IMPLICIT_DEF
+; CHECK: %{{[0-9]+}}:_(p0) = G_IMPLICIT_DEF
; CHECK-NEXT: RET_ReallyLR
%x = alloca %t
%inv = call ptr @llvm.invariant.start.p0(i64 8, ptr %x)
diff --git a/llvm/test/CodeGen/AMDGPU/GlobalISel/promote-dependency-on-invariant-result.ll b/llvm/test/CodeGen/AMDGPU/GlobalISel/promote-dependency-on-invariant-result.ll
new file mode 100644
index 000000000000000..c922ced4151e1da
--- /dev/null
+++ b/llvm/test/CodeGen/AMDGPU/GlobalISel/promote-dependency-on-invariant-result.ll
@@ -0,0 +1,37 @@
+; NOTE: Assertions have been autogenerated by utils/update_mir_test_checks.py UTC_ARGS: --version 5
+; RUN: llc -mtriple=amdgcn -mcpu=gfx90a -O0 -global-isel=true --stop-after=instruction-select --verify-machineinstrs -o - %s | FileCheck %s
+target datalayout = "A5"
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+declare ptr @llvm.invariant.start.p5(i64 immarg, ptr addrspace(5) nocapture) #0
+
+; Function Attrs: nocallback nofree nosync nounwind willreturn memory(argmem: readwrite)
+declare void @llvm.invariant.end.p5(ptr, i64 immarg, ptr addrspace(5) nocapture) #0
+
+; Function Attrs: nounwind
+define amdgpu_kernel void @use_invariant_promotable_lds(ptr addrspace(1) %arg) #2 {
+ ; CHECK-LABEL: name: use_invariant_promotable_lds
+ ; CHECK: bb.1.bb:
+ ; CHECK-NEXT: liveins: $sgpr4_sgpr5
+ ; CHECK-NEXT: {{ $}}
+ ; CHECK-NEXT: [[COPY:%[0-9]+]]:sreg_64 = COPY $sgpr4_sgpr5
+ ; CHECK-NEXT: early-clobber %13:sreg_64_xexec = S_LOAD_DWORDX2_IMM_ec [[COPY]], 36, 0 :: (dereferenceable invariant load (p1) from %ir.arg.kernarg.offset, align 4, addrspace 4)
+ ; CHECK-NEXT: [[S_LOAD_DWORD_IMM:%[0-9]+]]:sreg_32_xm0_xexec = S_LOAD_DWORD_IMM %13, 0, 0 :: ("amdgpu-noclobber" load (s32) from %ir.arg.load, addrspace 1)
+ ; CHECK-NEXT: [[DEF:%[0-9]+]]:sreg_64 = IMPLICIT_DEF
+ ; CHECK-NEXT: [[COPY1:%[0-9]+]]:vgpr_32 = COPY [[S_LOAD_DWORD_IMM]]
+ ; CHECK-NEXT: [[COPY2:%[0-9]+]]:vreg_64_align2 = COPY [[DEF]]
+ ; CHECK-NEXT: FLAT_STORE_DWORD [[COPY2]], [[COPY1]], 0, 0, implicit $exec, implicit $flat_scr :: (store (s32) into %ir.tmpI)
+ ; CHECK-NEXT: S_ENDPGM 0
+bb:
+ %i = load i32, ptr addrspace(1) %arg, align 4
+ %tmp = alloca i32, align 4, addrspace(5)
+ %tmpI = call ptr @llvm.invariant.start.p5(i64 4, ptr addrspace(5) %tmp) #3
+ call void @llvm.invariant.end.p5(ptr %tmpI, i64 4, ptr addrspace(5) %tmp) #3
+ store i32 %i, ptr %tmpI, align 4
+ ret void
+}
+
+attributes #0 = { nocallback nofree nosync nounwind willreturn memory(argmem: readwrite) }
+attributes #1 = { nocallback nofree nosync nounwind speculatable willreturn memory(inaccessiblemem: readwrite) }
+attributes #2 = { nounwind }
+attributes #3 = { nounwind memory(argmem: readwrite) }
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