[PATCH] D42417: [SCEV] Fix isLoopEntryGuardedByCond
Serguei Katkov via Phabricator via llvm-commits
llvm-commits at lists.llvm.org
Tue Jan 23 05:20:07 PST 2018
skatkov created this revision.
skatkov added reviewers: sanjoy, mkazantsev, anna, dorit, reames.
If LHS or RHS are not available at loop entry then
isLoopEntryGuardedByCond should answer false.
Just implement it.
https://reviews.llvm.org/D42417
Files:
lib/Analysis/ScalarEvolution.cpp
test/Transforms/IndVarSimplify/inner-loop.ll
Index: test/Transforms/IndVarSimplify/inner-loop.ll
===================================================================
--- /dev/null
+++ test/Transforms/IndVarSimplify/inner-loop.ll
@@ -0,0 +1,54 @@
+; RUN: opt < %s -indvars -S | FileCheck %s
+
+; This is regression test for the bug in ScalarEvolution::isKnownPredicate.
+; It does not check whether SCEV is available at loop entry before invoking
+; and utility function isLoopEntryGuardedByCond and that leads to miscompile.
+
+target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128-ni:1"
+target triple = "x86_64-unknown-linux-gnu"
+
+declare void @foo(i64)
+declare void @bar(i32)
+
+define void @test(i8* %arr) {
+entry:
+ br label %outer_header
+
+outer_header:
+ %i = phi i32 [40, %entry], [%i.next, %outer_latch]
+ %i.64 = sext i32 %i to i64
+ br label %inner_header
+
+inner_header:
+ %j = phi i32 [27, %outer_header], [%j.next, %inner_backedge]
+ %j1 = zext i32 %j to i64
+; The next 4 lines are required for avoid widening of %j and
+; SCEV at %cmp would not be AddRec.
+ %gep = getelementptr inbounds i8, i8* %arr, i64 %j1
+ %ld = load i8, i8* %gep
+ %ec = icmp eq i8 %ld, 0
+ br i1 %ec, label %return, label %inner_backedge
+
+inner_backedge:
+ %cmp = icmp ult i32 %j, %i
+ %s = select i1 %cmp, i32 %i, i32 %j
+; Select should not be simplified because if
+; %i == 26 and %j == 27, %s should be equal to %j.
+; In case of a bug the instruction is simplified to
+; %s = select i1 true, i32 %0, i32 %j
+; CHECK-NOT: %s = select i1 true
+ call void @bar(i32 %s)
+ %j.next = add nsw i32 %j, -2
+ %cond = icmp ult i32 %j, 3
+ br i1 %cond, label %outer_latch, label %inner_header
+
+outer_latch:
+ %i.next = add i32 %i, -1
+ %cond2 = icmp sgt i32 %i.next, 13
+; This line is just for forcing widening of %i
+ call void @foo(i64 %i.64)
+ br i1 %cond2, label %outer_header, label %return
+
+return:
+ ret void
+}
Index: lib/Analysis/ScalarEvolution.cpp
===================================================================
--- lib/Analysis/ScalarEvolution.cpp
+++ lib/Analysis/ScalarEvolution.cpp
@@ -9062,6 +9062,10 @@
// (interprocedural conditions notwithstanding).
if (!L) return false;
+ // Both LHS and RHS must be available at loop entry.
+ if (!isAvailableAtLoopEntry(LHS, L) || !isAvailableAtLoopEntry(RHS, L))
+ return false;
+
if (isKnownPredicateViaConstantRanges(Pred, LHS, RHS))
return true;
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