[llvm] 43eafc0 - [llvm][gvn-sink] Don't try to sink inline asm (#138414)

[via llvm-commits]

Author: Paul Kirth
Date: 2025-05-05T18:16:33-07:00
New Revision: 43eafc0c4aca0b2fd159c09d4b162c1941b4f4ed

URL: https://github.com/llvm/llvm-project/commit/43eafc0c4aca0b2fd159c09d4b162c1941b4f4ed
DIFF: https://github.com/llvm/llvm-project/commit/43eafc0c4aca0b2fd159c09d4b162c1941b4f4ed.diff

LOG: [llvm][gvn-sink] Don't try to sink inline asm (#138414)

Fixes #138345. Before this patch, gvn-sink would try to sink inline
assembly statements. Other GVN passes avoid them (see
https://github.com/llvm/llvm-project/blob/b4fac94181c4cf17dbb7ecc2ae975712b0e4a6d1/llvm/lib/Transforms/Scalar/GVN.cpp#L2932
Similarly, gvn-sink should skip these instructions, since they are not
safe to move. To do this, we update the early exit in
canReplaceOperandWithVariable, since it should have caught this case.
It's more efficient to also skip numbering in GVNSink if the instruction
is InlineAsm, but that should be infrequent.

The test added is reduced from a failure when compiling Fuchsia with
gvn-sink.

Added: 
    llvm/test/Transforms/GVNSink/pr138345.ll

Modified: 
    llvm/lib/Transforms/Utils/Local.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Utils/Local.cpp b/llvm/lib/Transforms/Utils/Local.cpp
index 809a0d7ebeea6..ce03bc066c6e2 100644
--- a/llvm/lib/Transforms/Utils/Local.cpp
+++ b/llvm/lib/Transforms/Utils/Local.cpp
@@ -4225,8 +4225,9 @@ bool llvm::canReplaceOperandWithVariable(const Instruction *I, unsigned OpIdx) {
     return false;
 
   // Early exit.
-  if (!isa<Constant>(I->getOperand(OpIdx)))
+  if (!isa<Constant, InlineAsm>(I->getOperand(OpIdx))) {
     return true;
+  }
 
   switch (I->getOpcode()) {
   default:

diff  --git a/llvm/test/Transforms/GVNSink/pr138345.ll b/llvm/test/Transforms/GVNSink/pr138345.ll
new file mode 100644
index 0000000000000..7a29d25d84eeb
--- /dev/null
+++ b/llvm/test/Transforms/GVNSink/pr138345.ll
@@ -0,0 +1,46 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN:  opt -passes="gvn-sink" -S %s | FileCheck %s
+
+;; See https://github.com/llvm/llvm-project/issues/138345 for details.
+;; The program below used to crash due to taking the address of the inline asm.
+;; gvn-sink shouldn't do anything in this case, so test that the pass no longer
+;; generates invalid IR and no longer crashes.
+
+define void @c(i64 %num, ptr %ptr) {
+; CHECK-LABEL: define void @c(
+; CHECK-SAME: i64 [[NUM:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*:]]
+; CHECK-NEXT:    switch i64 [[NUM]], label %[[SW_EPILOG:.*]] [
+; CHECK-NEXT:      i64 1, label %[[SW_BB:.*]]
+; CHECK-NEXT:      i64 0, label %[[SW_BB1:.*]]
+; CHECK-NEXT:    ]
+; CHECK:       [[SW_BB]]:
+; CHECK-NEXT:    [[TMP1:%.*]] = load i8, ptr [[PTR]], align 1
+; CHECK-NEXT:    call void asm sideeffect "", "r,r,~{dirflag},~{fpsr},~{flags}"(i8 [[TMP1]], ptr @c)
+; CHECK-NEXT:    br label %[[SW_EPILOG]]
+; CHECK:       [[SW_BB1]]:
+; CHECK-NEXT:    [[TMP2:%.*]] = load i8, ptr [[PTR]], align 1
+; CHECK-NEXT:    call void asm sideeffect "movdqu 0 [[XMM0:%.*]] \0A\09", "r,r,~{dirflag},~{fpsr},~{flags}"(i8 [[TMP2]], ptr @c)
+; CHECK-NEXT:    br label %[[SW_EPILOG]]
+; CHECK:       [[SW_EPILOG]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  switch i64 %num, label %sw.epilog [
+  i64 1, label %sw.bb
+  i64 0, label %sw.bb1
+  ]
+
+sw.bb:                                            ; preds = %entry
+  %1 = load i8, ptr %ptr, align 1
+  call void asm sideeffect "", "r,r,~{dirflag},~{fpsr},~{flags}"(i8 %1, ptr @c)
+  br label %sw.epilog
+
+sw.bb1:                                           ; preds = %entry
+  %2 = load i8, ptr %ptr, align 1
+  call void asm sideeffect "movdqu 0 %xmm0           \0A\09", "r,r,~{dirflag},~{fpsr},~{flags}"(i8 %2, ptr @c)
+  br label %sw.epilog
+
+sw.epilog:                                        ; preds = %sw.bb1, %sw.bb, %entry
+  ret void
+}