[llvm] r219834 - Teach ScalarEvolution to sharpen range information.
Kostya Serebryany
kcc at google.com
Wed Oct 15 16:23:13 PDT 2014
This change seems to be causing a miscompile which makes sanitizer bots
red:
http://lab.llvm.org:8011/builders/sanitizer-x86_64-linux
I've confirmed by checking out r219834 (this revision) and r219833
(previous one) and running
ninja Asan-x86_64-inline-Test &&
./projects/compiler-rt/lib/asan/tests/Asan-x86_64-inline-Test
--gtest_filter=AddressSanitizerInterface.PushAndPopWithPoisoningTest
Please fix or revert ASAP.
--kcc
On Wed, Oct 15, 2014 at 12:25 PM, Sanjoy Das <sanjoy at playingwithpointers.com
> wrote:
> Author: sanjoy
> Date: Wed Oct 15 14:25:28 2014
> New Revision: 219834
>
> URL: http://llvm.org/viewvc/llvm-project?rev=219834&view=rev
> Log:
> Teach ScalarEvolution to sharpen range information.
>
> If x is known to have the range [a, b) in a loop predicated by (icmp
> ne x, a), its range can be sharpened to [a + 1, b). Get
> ScalarEvolution and hence IndVars to exploit this fact.
>
> This change triggers an optimization to widen-loop-comp.ll, so it had
> to be edited to get it to pass.
>
> phabricator: http://reviews.llvm.org/D5639
>
>
> Added:
> llvm/trunk/test/Transforms/IndVarSimplify/sharpen-range-metadata.ll
> Modified:
> llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> llvm/trunk/test/Transforms/IndVarSimplify/widen-loop-comp.ll
>
> Modified: llvm/trunk/lib/Analysis/ScalarEvolution.cpp
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Analysis/ScalarEvolution.cpp?rev=219834&r1=219833&r2=219834&view=diff
>
> ==============================================================================
> --- llvm/trunk/lib/Analysis/ScalarEvolution.cpp (original)
> +++ llvm/trunk/lib/Analysis/ScalarEvolution.cpp Wed Oct 15 14:25:28 2014
> @@ -6782,6 +6782,44 @@ bool ScalarEvolution::isImpliedCond(ICmp
> RHS, LHS, FoundLHS, FoundRHS);
> }
>
> + if (FoundPred == ICmpInst::ICMP_NE) {
> + // If we are predicated on something with range [a, b) known not
> + // equal to a, the range can be sharpened to [a + 1, b). Use this
> + // fact.
> + auto CheckRange = [this, Pred, LHS, RHS](const SCEV *C, const SCEV
> *V) {
> + if (!isa<SCEVConstant>(C)) return false;
> +
> + ConstantInt *CI = cast<SCEVConstant>(C)->getValue();
> + APInt Min = ICmpInst::isSigned(Pred) ?
> + getSignedRange(V).getSignedMin() :
> getUnsignedRange(V).getUnsignedMin();
> +
> + if (Min!= CI->getValue()) return false; // nothing to sharpen
> + Min++;
> +
> + // We know V >= Min, in the same signedness as in Pred. We can
> + // use this to simplify slt and ult. If the range had a single
> + // value, Min, we now know that FoundValue can never be true;
> + // and any answer is a correct answer.
> +
> + switch (Pred) {
> + case ICmpInst::ICMP_SGT:
> + case ICmpInst::ICMP_UGT:
> + return isImpliedCondOperands(Pred, LHS, RHS, V,
> getConstant(Min));
> +
> + default:
> + llvm_unreachable("don't call with predicates other than
> ICMP_SGT "
> + "and ICMP_UGT");
> + }
> + };
> +
> + if ((Pred == ICmpInst::ICMP_SGT) || (Pred == ICmpInst::ICMP_UGT)) {
> + // Inequality is reflexive -- check both the combinations.
> + if (CheckRange(FoundLHS, FoundRHS) || CheckRange(FoundRHS,
> FoundLHS)) {
> + return true;
> + }
> + }
> + }
> +
> // Check whether the actual condition is beyond sufficient.
> if (FoundPred == ICmpInst::ICMP_EQ)
> if (ICmpInst::isTrueWhenEqual(Pred))
>
> Added: llvm/trunk/test/Transforms/IndVarSimplify/sharpen-range-metadata.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/sharpen-range-metadata.ll?rev=219834&view=auto
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/sharpen-range-metadata.ll
> (added)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/sharpen-range-metadata.ll
> Wed Oct 15 14:25:28 2014
> @@ -0,0 +1,39 @@
> +;; RUN: opt -S < %s -indvars | FileCheck %s
> +
> +;; Check if llvm can narrow !range metadata based on loop entry
> +;; predicates.
> +
> +declare void @abort()
> +
> +define i1 @bounded_below(i32* nocapture readonly %buffer) {
> +entry:
> + %length = load i32* %buffer, !range !0
> + %entry.pred = icmp eq i32 %length, 0
> + br i1 %entry.pred, label %abort, label %loop.preheader
> +
> +loop.preheader:
> + br label %loop
> +
> +loop:
> + %idx = phi i32 [ %idx.inc, %loop.next ], [ 0, %loop.preheader ]
> + %oob.pred = icmp slt i32 %idx, %length
> + br i1 %oob.pred, label %loop.next, label %oob
> +; CHECK: br i1 true, label %loop.next, label %oob
> +
> +loop.next:
> + %idx.inc = add i32 %idx, 1
> + %exit.pred = icmp slt i32 %idx.inc, %length
> + br i1 %exit.pred, label %loop, label %abort.loopexit
> +
> +abort.loopexit:
> + br label %abort
> +
> +abort:
> + ret i1 false
> +
> +oob:
> + tail call void @abort()
> + ret i1 false
> +}
> +
> +!0 = metadata !{i32 0, i32 100}
>
> Modified: llvm/trunk/test/Transforms/IndVarSimplify/widen-loop-comp.ll
> URL:
> http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/IndVarSimplify/widen-loop-comp.ll?rev=219834&r1=219833&r2=219834&view=diff
>
> ==============================================================================
> --- llvm/trunk/test/Transforms/IndVarSimplify/widen-loop-comp.ll (original)
> +++ llvm/trunk/test/Transforms/IndVarSimplify/widen-loop-comp.ll Wed Oct
> 15 14:25:28 2014
> @@ -67,8 +67,7 @@ for.end:
> define void @test2([8 x i8]* %a, i8* %b, i8 %limit) {
> entry:
> %conv = zext i8 %limit to i32
> - %cmp23 = icmp eq i8 %limit, 0
> - br i1 %cmp23, label %for.cond1.preheader, label %for.cond1.preheader.us
> + br i1 undef, label %for.cond1.preheader, label %for.cond1.preheader.us
>
> for.cond1.preheader.us:
> %storemerge5.us = phi i32 [ 0, %entry ], [ %inc14.us, %for.inc13.us ]
>
>
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