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Add stride normalization to SCEV Normalize/Denormalize transformation.

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llvm-svn: 204161
This commit is contained in:
Michael Zolotukhin 2014-03-18 17:34:03 +00:00
parent b329156058
commit a73e842ea7
2 changed files with 30 additions and 4 deletions
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29
lib/Analysis/ScalarEvolutionNormalization.cpp
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@ -131,7 +131,10 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
// expression: {-2,+,1,+,2} + {1,+,2} => {-1,+,3,+,2}
if (AR->isAffine() &&
IVUseShouldUsePostIncValue(User, OperandValToReplace, L, &DT)) {
Result = SE.getMinusSCEV(Result, AR->getStepRecurrence(SE));
const SCEV *TransformedStep =
TransformSubExpr(AR->getStepRecurrence(SE),
User, OperandValToReplace);
Result = SE.getMinusSCEV(Result, TransformedStep);
Loops.insert(L);
}
#if 0
@ -144,6 +147,20 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
#endif
break;
case Normalize:
// We want to normalize step expression, because otherwise we might not be
// able to denormalize to the original expression.
//
// Here is an example what will happen if we don't normalize step:
// ORIGINAL ISE:
// {(100 /u {1,+,1}<%bb16>),+,(100 /u {1,+,1}<%bb16>)}<%bb25>
// NORMALIZED ISE:
// {((-1 * (100 /u {1,+,1}<%bb16>)) + (100 /u {0,+,1}<%bb16>)),+,
// (100 /u {0,+,1}<%bb16>)}<%bb25>
// DENORMALIZED BACK ISE:
// {((2 * (100 /u {1,+,1}<%bb16>)) + (-1 * (100 /u {2,+,1}<%bb16>))),+,
// (100 /u {1,+,1}<%bb16>)}<%bb25>
// Note that the initial value changes after normalization +
// denormalization, which isn't correct.
if (Loops.count(L)) {
const SCEV *TransformedStep =
TransformSubExpr(AR->getStepRecurrence(SE),
@ -157,8 +174,14 @@ TransformImpl(const SCEV *S, Instruction *User, Value *OperandValToReplace) {
#endif
break;
case Denormalize:
if (Loops.count(L))
Result = cast<SCEVAddRecExpr>(Result)->getPostIncExpr(SE);
// Here we want to normalize step expressions for the same reasons, as
// stated above.
if (Loops.count(L)) {
const SCEV *TransformedStep =
TransformSubExpr(AR->getStepRecurrence(SE),
User, OperandValToReplace);
Result = SE.getAddExpr(Result, TransformedStep);
}
break;
}
return Result;

5
test/CodeGen/X86/lsr-normalization.ll
View File

@ -1,4 +1,5 @@
; RUN: llc < %s -march=x86-64 | FileCheck %s
; REQUIRES: asserts
; RUN: llc -debug < %s -march=x86-64 2>&1 | FileCheck %s
; rdar://8168938
; This testcase involves SCEV normalization with the exit value from
@ -6,6 +7,8 @@
; loop. The expression should be properly normalized and simplified,
; and require only a single division.
; CHECK-NOT: DISCARDING (NORMALIZATION ISN'T INVERTIBLE)
; CHECK: _main:
; CHECK: div
; CHECK-NOT: div