76 lines
2.6 KiB
Diff
76 lines
2.6 KiB
Diff
Pull in r223171 from upstream llvm trunk (by Michael Zolotukhin):
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PR21302. Vectorize only bottom-tested loops.
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rdar://problem/18886083
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This fixes a bug in the llvm vectorizer, which could sometimes cause
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vectorized loops to perform an additional iteration, leading to possible
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buffer overruns. Symptoms of this, which are usually segfaults, were
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first noticed when building gcc ports, here:
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https://lists.freebsd.org/pipermail/freebsd-ports/2014-September/095466.html
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https://lists.freebsd.org/pipermail/freebsd-toolchain/2014-September/001211.html
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Note: because this is applied on top of llvm/clang 3.5.0, this fix is
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slightly different from the one just checked into head in r275633.
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Introduced here: http://svnweb.freebsd.org/changeset/base/275635
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Index: lib/Transforms/Vectorize/LoopVectorize.cpp
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===================================================================
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--- lib/Transforms/Vectorize/LoopVectorize.cpp (revision 21)
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+++ lib/Transforms/Vectorize/LoopVectorize.cpp (revision 22)
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@@ -3466,6 +3466,15 @@ bool LoopVectorizationLegality::canVectorize() {
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return false;
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}
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+ // We only handle bottom-tested loops, i.e. loop in which the condition is
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+ // checked at the end of each iteration. With that we can assume that all
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+ // instructions in the loop are executed the same number of times.
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+ if (TheLoop->getExitingBlock() != TheLoop->getLoopLatch()) {
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+ emitAnalysis(
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+ Report() << "loop control flow is not understood by vectorizer");
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+ return false;
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+ }
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+
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// We need to have a loop header.
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DEBUG(dbgs() << "LV: Found a loop: " <<
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TheLoop->getHeader()->getName() << '\n');
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Index: test/Transforms/LoopVectorize/loop-form.ll
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===================================================================
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--- test/Transforms/LoopVectorize/loop-form.ll (revision 0)
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+++ test/Transforms/LoopVectorize/loop-form.ll (revision 22)
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@@ -0,0 +1,31 @@
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+; RUN: opt -S -loop-vectorize < %s | FileCheck %s
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+target datalayout = "e-m:o-i64:64-f80:128-n8:16:32:64-S128"
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+
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+; Check that we vectorize only bottom-tested loops.
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+; This is a reduced testcase from PR21302.
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+;
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+; rdar://problem/18886083
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+
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+%struct.X = type { i32, i16 }
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+; CHECK-LABEL: @foo(
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+; CHECK-NOT: vector.body
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+
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+define void @foo(i32 %n) {
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+entry:
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+ br label %for.cond
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+
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+for.cond:
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+ %i = phi i32 [ 0, %entry ], [ %inc, %for.body ]
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+ %cmp = icmp slt i32 %i, %n
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+ br i1 %cmp, label %for.body, label %if.end
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+
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+for.body:
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+ %iprom = sext i32 %i to i64
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+ %b = getelementptr inbounds %struct.X* undef, i64 %iprom, i32 1
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+ store i16 0, i16* %b, align 4
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+ %inc = add nsw i32 %i, 1
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+ br label %for.cond
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+
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+if.end:
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+ ret void
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+}
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