[PATCH] D62531: SpeculateAroundPHIs: Respect convergent

[Matt Arsenault via Phabricator via llvm-commits]

arsenm created this revision.
arsenm added a reviewer: chandlerc.
Herald added subscribers: nhaehnle, wdng, jvesely.

This would break for speculatable and convergent intrinsic calls.


https://reviews.llvm.org/D62531

Files:
  lib/Transforms/Scalar/SpeculateAroundPHIs.cpp
  test/Transforms/SpeculateAroundPHIs/AMDGPU/convergent.ll
  test/Transforms/SpeculateAroundPHIs/AMDGPU/lit.local.cfg


Index: test/Transforms/SpeculateAroundPHIs/AMDGPU/lit.local.cfg
===================================================================
--- /dev/null
+++ test/Transforms/SpeculateAroundPHIs/AMDGPU/lit.local.cfg
@@ -0,0 +1,3 @@
+if not 'AMDGPU' in config.root.targets:
+    config.unsupported = True
+
Index: test/Transforms/SpeculateAroundPHIs/AMDGPU/convergent.ll
===================================================================
--- /dev/null
+++ test/Transforms/SpeculateAroundPHIs/AMDGPU/convergent.ll
@@ -0,0 +1,35 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes=spec-phis < %s | FileCheck %s
+; Make sure convergent and noduplicate calls aren't duplicated.
+
+declare i32 @llvm.amdgcn.wwm.i32(i32) #0
+
+define i32 @test_convergent(i1 %flag, i32 %arg) #0 {
+; CHECK-LABEL: @test_convergent(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    br i1 [[FLAG:%.*]], label [[A:%.*]], label [[B:%.*]]
+; CHECK:       a:
+; CHECK-NEXT:    br label [[EXIT:%.*]]
+; CHECK:       b:
+; CHECK-NEXT:    br label [[EXIT]]
+; CHECK:       exit:
+; CHECK-NEXT:    [[P:%.*]] = phi i32 [ 7, [[A]] ], [ 11, [[B]] ]
+; CHECK-NEXT:    [[SUM:%.*]] = call i32 @llvm.amdgcn.wwm.i32(i32 [[P]])
+; CHECK-NEXT:    ret i32 [[SUM]]
+;
+entry:
+  br i1 %flag, label %a, label %b
+
+a:
+  br label %exit
+
+b:
+  br label %exit
+
+exit:
+  %p = phi i32 [ 7, %a ], [ 11, %b ]
+  %sum = call i32 @llvm.amdgcn.wwm.i32(i32 %p)
+  ret i32 %sum
+}
+
+attributes #0 = { nounwind readnone convergent speculatable }
Index: lib/Transforms/Scalar/SpeculateAroundPHIs.cpp
===================================================================
--- lib/Transforms/Scalar/SpeculateAroundPHIs.cpp
+++ lib/Transforms/Scalar/SpeculateAroundPHIs.cpp
@@ -67,6 +67,14 @@
       return false;
     }
 
+    if (auto CS = ImmutableCallSite(UI)) {
+      if (CS.isConvergent() || CS.cannotDuplicate()) {
+        LLVM_DEBUG(dbgs() << "  Unsafe: convergent "
+                   "callsite cannot de duplicated: " << *UI << '\n');
+        return false;
+      }
+    }
+
     // FIXME: This check is much too conservative. We're not going to move these
     // instructions onto new dynamic paths through the program unless there is
     // a call instruction between the use and the PHI node. And memory isn't


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