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When analyzing loop exit conditions combined with and and or, don't

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make any assumptions about when the two conditions will agree on when
to permit the loop to exit. This fixes PR7845.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110758 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Dan Gohman 2010-08-11 00:12:36 +00:00
parent f4452c37d0
commit 4ee87398e8
2 changed files with 52 additions and 16 deletions
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26
lib/Analysis/ScalarEvolution.cpp
View File

@ -3854,14 +3854,13 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCond(const Loop *L,
else
MaxBECount = getUMinFromMismatchedTypes(BTI0.Max, BTI1.Max);
} else {
// Both conditions must be true for the loop to exit.
// Both conditions must be true at the same time for the loop to exit.
// For now, be conservative.
assert(L->contains(FBB) && "Loop block has no successor in loop!");
if (BTI0.Exact != getCouldNotCompute() &&
BTI1.Exact != getCouldNotCompute())
BECount = getUMaxFromMismatchedTypes(BTI0.Exact, BTI1.Exact);
if (BTI0.Max != getCouldNotCompute() &&
BTI1.Max != getCouldNotCompute())
MaxBECount = getUMaxFromMismatchedTypes(BTI0.Max, BTI1.Max);
if (BTI0.Max == BTI1.Max)
MaxBECount = BTI0.Max;
if (BTI0.Exact == BTI1.Exact)
BECount = BTI0.Exact;
}
return BackedgeTakenInfo(BECount, MaxBECount);
@ -3889,14 +3888,13 @@ ScalarEvolution::ComputeBackedgeTakenCountFromExitCond(const Loop *L,
else
MaxBECount = getUMinFromMismatchedTypes(BTI0.Max, BTI1.Max);
} else {
// Both conditions must be false for the loop to exit.
// Both conditions must be false at the same time for the loop to exit.
// For now, be conservative.
assert(L->contains(TBB) && "Loop block has no successor in loop!");
if (BTI0.Exact != getCouldNotCompute() &&
BTI1.Exact != getCouldNotCompute())
BECount = getUMaxFromMismatchedTypes(BTI0.Exact, BTI1.Exact);
if (BTI0.Max != getCouldNotCompute() &&
BTI1.Max != getCouldNotCompute())
MaxBECount = getUMaxFromMismatchedTypes(BTI0.Max, BTI1.Max);
if (BTI0.Max == BTI1.Max)
MaxBECount = BTI0.Max;
if (BTI0.Exact == BTI1.Exact)
BECount = BTI0.Exact;
}
return BackedgeTakenInfo(BECount, MaxBECount);

42
test/Analysis/ScalarEvolution/max-trip-count.ll
View File

@ -1,8 +1,9 @@
; RUN: opt < %s -analyze -scalar-evolution \
; RUN: | grep {\{%d,+,\[^\{\}\]\*\}<%bb>}
; RUN: opt < %s -analyze -scalar-evolution | FileCheck %s
; ScalarEvolution should be able to understand the loop and eliminate the casts.
; CHECK: {%d,+,sizeof(i32)}
define void @foo(i32* nocapture %d, i32 %n) nounwind {
entry:
%0 = icmp sgt i32 %n, 0 ; <i1> [#uses=1]
@ -32,3 +33,40 @@ bb1.return_crit_edge: ; preds = %bb1
return: ; preds = %bb1.return_crit_edge, %entry
ret void
}
; ScalarEvolution should be able to find the maximum tripcount
; of this multiple-exit loop, and if it doesn't know the exact
; count, it should say so.
; PR7845
; CHECK: Loop %for.cond: <multiple exits> Unpredictable backedge-taken count.
; CHECK: Loop %for.cond: max backedge-taken count is 5
@.str = private constant [4 x i8] c"%d\0A\00" ; <[4 x i8]*> [#uses=2]
define i32 @main() nounwind {
entry:
br label %for.cond
for.cond: ; preds = %for.inc, %entry
%g_4.0 = phi i32 [ 0, %entry ], [ %add, %for.inc ] ; <i32> [#uses=5]
%cmp = icmp slt i32 %g_4.0, 5 ; <i1> [#uses=1]
br i1 %cmp, label %for.body, label %for.end
for.body: ; preds = %for.cond
%conv = trunc i32 %g_4.0 to i16 ; <i16> [#uses=1]
%tobool.not = icmp eq i16 %conv, 0 ; <i1> [#uses=1]
%tobool3 = icmp ne i32 %g_4.0, 0 ; <i1> [#uses=1]
%or.cond = and i1 %tobool.not, %tobool3 ; <i1> [#uses=1]
br i1 %or.cond, label %for.end, label %for.inc
for.inc: ; preds = %for.body
%add = add nsw i32 %g_4.0, 1 ; <i32> [#uses=1]
br label %for.cond
for.end: ; preds = %for.body, %for.cond
%call = call i32 (i8*, ...)* @printf(i8* getelementptr inbounds ([4 x i8]* @.str, i64 0, i64 0), i32 %g_4.0) nounwind ; <i32> [#uses=0]
ret i32 0
}
declare i32 @printf(i8*, ...)