[PATCH] D117303: [LoopUnswitch] Deny loop unswitch if its body contains volatile inline asm

[Daniil Kovalev via Phabricator via llvm-commits]

kovdan01 created this revision.
kovdan01 added reviewers: tra, jaykang10, fhahn.
Herald added a subscriber: hiraditya.
kovdan01 requested review of this revision.
Herald added a project: LLVM.
Herald added a subscriber: llvm-commits.

Volatile inline asm might contain convergent insructions.
Unswitching such loops breaks code correctness for targets like NVPTX.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D117303

Files:
  llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
  llvm/test/Transforms/LoopUnswitch/convergent-hoist-modified.ll


Index: llvm/test/Transforms/LoopUnswitch/convergent-hoist-modified.ll
===================================================================
--- llvm/test/Transforms/LoopUnswitch/convergent-hoist-modified.ll
+++ llvm/test/Transforms/LoopUnswitch/convergent-hoist-modified.ll
@@ -5,17 +5,21 @@
 ; Modified status. This was caught by the pass return status check that is
 ; hidden under EXPENSIVE_CHECKS.
 
-; CHECK-LABEL: entry:
-; CHECK-NEXT: %0 = call i32 @llvm.objectsize.i32.p0i8(i8* bitcast (%struct.anon* @b to i8*), i1 false, i1 false, i1 false)
-; CHECK-NEXT: %1 = icmp uge i32 %0, 1
-; CHECK-NEXT: br label %for.cond
-
 %struct.anon = type { i16 }
 
 @b = global %struct.anon zeroinitializer, align 1
 
+; Function Attrs: nounwind readnone speculatable willreturn
+declare i32 @llvm.objectsize.i32.p0i8(i8*, i1 immarg, i1 immarg, i1 immarg) #1
+
+declare void @conv() convergent
+
 ; Function Attrs: nounwind
 define i16 @c() #0 {
+; CHECK-LABEL: entry:
+; CHECK-NEXT: %0 = call i32 @llvm.objectsize.i32.p0i8(i8* bitcast (%struct.anon* @b to i8*), i1 false, i1 false, i1 false)
+; CHECK-NEXT: %1 = icmp uge i32 %0, 1
+; CHECK-NEXT: br label %for.cond
 entry:
   br label %for.cond
 
@@ -33,10 +37,28 @@
   br label %for.cond
 }
 
-; Function Attrs: nounwind readnone speculatable willreturn
-declare i32 @llvm.objectsize.i32.p0i8(i8*, i1 immarg, i1 immarg, i1 immarg) #1
+; Function Attrs: nounwind
+define i16 @d() #0 {
+; CHECK-LABEL: entry:
+; CHECK-NEXT: %0 = call i32 @llvm.objectsize.i32.p0i8(i8* bitcast (%struct.anon* @b to i8*), i1 false, i1 false, i1 false)
+; CHECK-NEXT: %1 = icmp uge i32 %0, 1
+; CHECK-NEXT: br label %for.cond
+entry:
+  br label %for.cond
 
-declare void @conv() convergent
+for.cond:                                         ; preds = %cont, %entry
+  br label %for.inc
+
+for.inc:                                          ; preds = %for.cond
+  %0 = call i32 @llvm.objectsize.i32.p0i8(i8* bitcast (%struct.anon* @b to i8*), i1 false, i1 false, i1 false)
+  %1 = icmp uge i32 %0, 1
+  br i1 %1, label %cont, label %cont
+
+cont:                                             ; preds = %for.inc
+  call void asm sideeffect "; some convergent instructions here", ""()
+  %2 = load i16, i16* getelementptr inbounds (%struct.anon, %struct.anon* @b, i32 0, i32 0), align 1
+  br label %for.cond
+}
 
 attributes #0 = { nounwind }
 attributes #1 = { nounwind readnone speculatable willreturn }
Index: llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
+++ llvm/lib/Transforms/Scalar/LoopUnswitch.cpp
@@ -51,6 +51,7 @@
 #include "llvm/IR/Dominators.h"
 #include "llvm/IR/Function.h"
 #include "llvm/IR/IRBuilder.h"
+#include "llvm/IR/InlineAsm.h"
 #include "llvm/IR/InstrTypes.h"
 #include "llvm/IR/Instruction.h"
 #include "llvm/IR/Instructions.h"
@@ -697,6 +698,11 @@
         continue;
       if (CB->isConvergent())
         return Changed;
+      // Volatile inline asm may contain convergent instructions
+      // e.g., PTX shfl.sync, so rejecting them for correctness
+      if (auto *Asm = dyn_cast<InlineAsm>(CB->getCalledOperand()))
+        if (Asm->hasSideEffects())
+          return Changed;
       if (auto *II = dyn_cast<InvokeInst>(&I))
         if (!II->getUnwindDest()->canSplitPredecessors())
           return Changed;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D117303.399955.patch
Type: text/x-patch
Size: 3378 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20220114/a3eb36d2/attachment.bin>