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Fix LSR: don't normalize quadratic recurrences.

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Partial fix for PR17459: wrong code at -O3 on x86_64-linux-gnu
(affecting trunk and 3.3)

ScalarEvolutionNormalization was attempting to normalize by adding and
subtracting strides. Chained recurrences don't work that way.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@193437 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Andrew Trick 2013-10-25 21:35:52 +00:00
parent 0f978ea459
commit 8aa8cea3e9
2 changed files with 51 additions and 11 deletions
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18
lib/Analysis/ScalarEvolutionNormalization.cpp
View File

@ -119,11 +119,19 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
const SCEV *Result = SE.getAddRecExpr(Operands, L, SCEV::FlagAnyWrap);
switch (Kind) {
case NormalizeAutodetect:
if (IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
const SCEV *TransformedStep =
TransformSubExpr(AR->getStepRecurrence(SE),
User, OperandValToReplace);
Result = SE.getMinusSCEV(Result, TransformedStep);
// Normalize this SCEV by subtracting the expression for the final step.
// We only allow affine AddRecs to be normalized, otherwise we would not
// be able to correctly denormalize.
// e.g. {1,+,3,+,2} == {-2,+,1,+,2} + {3,+,2}
// Normalized form: {-2,+,1,+,2}
// Denormalized form: {1,+,3,+,2}
//
// However, denormalization would use the a different step expression than
// normalization (see getPostIncExpr), generating the wrong final
// expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
if (AR->isAffine() &&
IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE));
Loops.insert(L);
}
#if 0

44
test/Transforms/LoopStrengthReduce/quadradic-exit-value.ll
View File

@ -1,18 +1,50 @@
; RUN: opt < %s -analyze -iv-users | grep "{1,+,3,+,2}<%loop> (post-inc with loop %loop)"
; RUN: opt < %s -analyze -iv-users | FileCheck %s
; The value of %r is dependent on a polynomial iteration expression.
;
; CHECK-LABEL: IV Users for loop %foo.loop
; CHECK: {1,+,3,+,2}<%foo.loop>
define i64 @foo(i64 %n) {
entry:
br label %loop
br label %foo.loop
loop:
%indvar = phi i64 [ 0, %entry ], [ %indvar.next, %loop ]
foo.loop:
%indvar = phi i64 [ 0, %entry ], [ %indvar.next, %foo.loop ]
%indvar.next = add i64 %indvar, 1
%c = icmp eq i64 %indvar.next, %n
br i1 %c, label %exit, label %loop
br i1 %c, label %exit, label %foo.loop
exit:
%r = mul i64 %indvar.next, %indvar.next
ret i64 %r
}
; PR15470: LSR miscompile. The test2 function should return '1'.
;
; SCEV does not know how to denormalize chained recurrences, so make
; sure they aren't marked as post-inc users.
;
; CHECK-LABEL: IV Users for loop %test2.loop
; CHECK: %sext.us = {0,+,(16777216 + (-16777216 * %sub.us)),+,33554432}<%test2.loop> in %f = ashr i32 %sext.us, 24
define i32 @test2() {
entry:
br label %test2.loop
test2.loop:
%inc1115.us = phi i32 [ 0, %entry ], [ %inc11.us, %test2.loop ]
%inc11.us = add nsw i32 %inc1115.us, 1
%cmp.us = icmp slt i32 %inc11.us, 2
br i1 %cmp.us, label %test2.loop, label %for.end
for.end:
%tobool.us = icmp eq i32 %inc1115.us, 0
%sub.us = select i1 %tobool.us, i32 0, i32 0
%mul.us = shl i32 %inc1115.us, 24
%sub.cond.us = sub nsw i32 %inc1115.us, %sub.us
%sext.us = mul i32 %mul.us, %sub.cond.us
%f = ashr i32 %sext.us, 24
br label %exit
exit:
ret i32 %f
}