[llvm] r261540 - Don't tail-duplicate blocks that contain convergent instructions.
Justin Lebar via llvm-commits
llvm-commits at lists.llvm.org
Mon Feb 22 09:50:53 PST 2016
Author: jlebar
Date: Mon Feb 22 11:50:52 2016
New Revision: 261540
URL: http://llvm.org/viewvc/llvm-project?rev=261540&view=rev
Log:
Don't tail-duplicate blocks that contain convergent instructions.
Summary:
Convergent instrs shouldn't be made control-dependent on other values,
but this is basically the whole point of tail duplication. So just bail
if we see a convergent instruction.
Reviewers: iteratee
Subscribers: jholewinski, jhen, hfinkel, tra, jingyue, llvm-commits
Differential Revision: http://reviews.llvm.org/D17320
Added:
llvm/trunk/test/CodeGen/NVPTX/TailDuplication-convergent.ll
Modified:
llvm/trunk/lib/CodeGen/TailDuplication.cpp
Modified: llvm/trunk/lib/CodeGen/TailDuplication.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/TailDuplication.cpp?rev=261540&r1=261539&r2=261540&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/TailDuplication.cpp (original)
+++ llvm/trunk/lib/CodeGen/TailDuplication.cpp Mon Feb 22 11:50:52 2016
@@ -590,6 +590,11 @@ TailDuplicatePass::shouldTailDuplicate(c
if (MI.isNotDuplicable())
return false;
+ // Convergent instructions can be duplicated only if doing so doesn't add
+ // new control dependencies, which is what we're going to do here.
+ if (MI.isConvergent())
+ return false;
+
// Do not duplicate 'return' instructions if this is a pre-regalloc run.
// A return may expand into a lot more instructions (e.g. reload of callee
// saved registers) after PEI.
Added: llvm/trunk/test/CodeGen/NVPTX/TailDuplication-convergent.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/NVPTX/TailDuplication-convergent.ll?rev=261540&view=auto
==============================================================================
--- llvm/trunk/test/CodeGen/NVPTX/TailDuplication-convergent.ll (added)
+++ llvm/trunk/test/CodeGen/NVPTX/TailDuplication-convergent.ll Mon Feb 22 11:50:52 2016
@@ -0,0 +1,45 @@
+; RUN: llc -O2 -tail-dup-size=100 -enable-tail-merge=0 < %s | FileCheck %s
+target triple = "nvptx64-nvidia-cuda"
+
+declare void @foo()
+declare void @llvm.cuda.syncthreads()
+
+; syncthreads shouldn't be duplicated.
+; CHECK: .func call_syncthreads
+; CHECK: bar.sync
+; CHECK-NOT: bar.sync
+define void @call_syncthreads(i32* %a, i32* %b, i1 %cond, i1 %cond2) nounwind {
+ br i1 %cond, label %L1, label %L2
+ br i1 %cond2, label %Ret, label %L1
+Ret:
+ ret void
+L1:
+ store i32 0, i32* %a
+ br label %L42
+L2:
+ store i32 1, i32* %a
+ br label %L42
+L42:
+ call void @llvm.cuda.syncthreads()
+ br label %Ret
+}
+
+; Check that call_syncthreads really does trigger tail duplication.
+; CHECK: .func call_foo
+; CHECK: call
+; CHECK: call
+define void @call_foo(i32* %a, i32* %b, i1 %cond, i1 %cond2) nounwind {
+ br i1 %cond, label %L1, label %L2
+ br i1 %cond2, label %Ret, label %L1
+Ret:
+ ret void
+L1:
+ store i32 0, i32* %a
+ br label %L42
+L2:
+ store i32 1, i32* %a
+ br label %L42
+L42:
+ call void @foo()
+ br label %Ret
+}
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