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fe3275edf3
Summary: There is currently a correctness issue when unrolling loops containing callbr's where their indirect targets are being updated correctly to the newly created labels, but their operands are not. This manifests in unrolled loops where the second and subsequent copies of callbr instructions have blockaddresses of the label from the first instance of the unrolled loop, which would result in nonsensical runtime control flow. For now, conservatively do not unroll the loop. In the future, I think we can pursue unrolling such loops provided we transform the cloned callbr's operands correctly. Such a transform and its legalities are being discussed in: https://reviews.llvm.org/D64101 Link: https://bugs.llvm.org/show_bug.cgi?id=42489 Link: https://groups.google.com/forum/#!topic/clang-built-linux/z-hRWP9KqPI Reviewers: fhahn, hfinkel, efriedma Reviewed By: fhahn, hfinkel, efriedma Subscribers: efriedma, hiraditya, zzheng, dmgreen, llvm-commits, pirama, kees, nathanchance, E5ten, craig.topper, chandlerc, glider, void, srhines Tags: #llvm Differential Revision: https://reviews.llvm.org/D64368 llvm-svn: 366130
52 lines
1.7 KiB
LLVM
52 lines
1.7 KiB
LLVM
; RUN: opt -loop-unroll -S %s | FileCheck %s
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; Check that the loop body exists.
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; CHECK: for.body
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; CHECK: if.then
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; CHECK: asm.fallthrough
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; CHECK: l_yes
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; CHECK: for.inc
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; Check that the loop body does not get unrolled. We could modify this test in
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; the future to support loop unrolling callbr's IFF we checked that the callbr
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; operands were unrolled/updated correctly, as today they are not.
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; CHECK-NOT: if.then.1
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; CHECK-NOT: asm.fallthrough.1
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; CHECK-NOT: l_yes.1
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; CHECK-NOT: for.inc.1
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; CHECK-NOT: if.then.2
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; CHECK-NOT: asm.fallthrough.2
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; CHECK-NOT: l_yes.2
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; CHECK-NOT: for.inc.2
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define dso_local void @d() {
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entry:
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br label %for.body
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for.cond.cleanup: ; preds = %for.inc
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ret void
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for.body: ; preds = %for.inc, %entry
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%e.04 = phi i32 [ 0, %entry ], [ %inc, %for.inc ]
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%tobool = icmp eq i32 %e.04, 0
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br i1 %tobool, label %for.inc, label %if.then
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if.then: ; preds = %for.body
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callbr void asm sideeffect "1: nop\0A\09.quad b, ${0:l}, $$5\0A\09", "X,~{dirflag},~{fpsr},~{flags}"(i8* blockaddress(@d, %l_yes))
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to label %asm.fallthrough [label %l_yes]
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asm.fallthrough: ; preds = %if.then
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br label %l_yes
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l_yes: ; preds = %asm.fallthrough, %if.then
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%call = tail call i32 (...) @g()
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br label %for.inc
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for.inc: ; preds = %for.body, %l_yes
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%inc = add nuw nsw i32 %e.04, 1
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%exitcond = icmp eq i32 %inc, 3
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br i1 %exitcond, label %for.cond.cleanup, label %for.body
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}
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declare dso_local i32 @g(...) local_unnamed_addr
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