[PATCH] D90391: [gvn] PRE needs to skip convergent intrinsics/calls.

[Michael Liao via Phabricator via llvm-commits]

hliao created this revision.
hliao added reviewers: fhahn, nikic, mkazantsev, jdoerfert, efriedma.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.
hliao requested review of this revision.

- As convergent intrinsics/calls could only be moved to control-equivalent blocks, or more precisely the same divergent branch, PRE needs to skip them.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D90391

Files:
  llvm/lib/Transforms/Scalar/GVN.cpp
  llvm/test/Transforms/GVN/pre-skip-convergent.ll


Index: llvm/test/Transforms/GVN/pre-skip-convergent.ll
===================================================================
--- /dev/null
+++ llvm/test/Transforms/GVN/pre-skip-convergent.ll
@@ -0,0 +1,25 @@
+; RUN: opt -S -gvn -o - %s | FileCheck %s
+
+; CHECK-LABEL: @foo
+; CHECK: pre:
+; CHECK-NOT: call i32 @llvm.convergent
+; CHECK: merge:
+define i32 @foo(i1 %cond, i32* %q, i32* %p) {
+entry:
+  %v0 = call i32 @llvm.convergent(i32 0)
+  store i32 %v0, i32* %q
+  br i1 %cond, label %pre, label %merge
+
+pre:
+  %t0 = load i32, i32* %p
+  br label %merge
+
+merge:
+  %m0 = phi i32 [ %t0, %pre ], [ 0, %entry ]
+  %r0 = call i32 @llvm.convergent(i32 %m0)
+  ret i32 %r0
+}
+
+declare i32 @llvm.convergent(i32) #0
+
+attributes #0 = { convergent nounwind readnone }
Index: llvm/lib/Transforms/Scalar/GVN.cpp
===================================================================
--- llvm/lib/Transforms/Scalar/GVN.cpp
+++ llvm/lib/Transforms/Scalar/GVN.cpp
@@ -2461,9 +2461,13 @@
     return false;
 
   // We don't currently value number ANY inline asm calls.
-  if (auto *CallB = dyn_cast<CallBase>(CurInst))
+  if (auto *CallB = dyn_cast<CallBase>(CurInst)) {
     if (CallB->isInlineAsm())
       return false;
+    // Don't do PRE on convergent calls.
+    if (CallB->isConvergent())
+      return false;
+  }
 
   uint32_t ValNo = VN.lookup(CurInst);
 


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