b92c8c22b9
Unswitching a loop on a non-trivial divergent branch is expensive since it serializes the execution of both version of the loop. But identifying a divergent branch needs divergence analysis, which is a function level analysis. The legacy pass manager handles this dependency by isolating such a loop transform and rerunning the required function analyses. This functionality is currently missing in the new pass manager, and there is no safe way for the SimpleLoopUnswitch pass to depend on DivergenceAnalysis. So we conservatively assume that all non-trivial branches are divergent if the target has divergence. Reviewed By: tra Differential Revision: https://reviews.llvm.org/D98958
46 lines
1.5 KiB
LLVM
46 lines
1.5 KiB
LLVM
; RUN: opt -mtriple=amdgcn-- -O3 -S %s | FileCheck %s
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; Check that loop unswitch does not happen if condition is divergent.
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; CHECK-LABEL: {{^}}define amdgpu_kernel void @divergent_unswitch
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; CHECK: entry:
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; CHECK: icmp
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; CHECK: [[IF_COND:%[a-z0-9]+]] = icmp {{.*}} 567890
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; CHECK: br label
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; CHECK: br i1 [[IF_COND]]
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define amdgpu_kernel void @divergent_unswitch(i32 * nocapture %out, i32 %n) {
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entry:
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%cmp9 = icmp sgt i32 %n, 0
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br i1 %cmp9, label %for.body.lr.ph, label %for.cond.cleanup
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for.body.lr.ph: ; preds = %entry
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%call = tail call i32 @llvm.amdgcn.workitem.id.x() #0
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%cmp2 = icmp eq i32 %call, 567890
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br label %for.body
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for.cond.cleanup.loopexit: ; preds = %for.inc
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br label %for.cond.cleanup
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for.cond.cleanup: ; preds = %for.cond.cleanup.loopexit, %entry
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ret void
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for.body: ; preds = %for.inc, %for.body.lr.ph
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%i.010 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
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br i1 %cmp2, label %if.then, label %for.inc
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if.then: ; preds = %for.body
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%arrayidx = getelementptr inbounds i32, i32 * %out, i32 %i.010
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store i32 %i.010, i32 * %arrayidx, align 4
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br label %for.inc
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for.inc: ; preds = %for.body, %if.then
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%inc = add nuw nsw i32 %i.010, 1
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%exitcond = icmp eq i32 %inc, %n
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br i1 %exitcond, label %for.cond.cleanup.loopexit, label %for.body
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}
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declare i32 @llvm.amdgcn.workitem.id.x() #0
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attributes #0 = { nounwind readnone }
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