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[IndVarSimplify] Eliminate zext of a signed IV when the IV is known to be non-negative

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Patch by Li Huang

Differential Revision: https://reviews.llvm.org/D18867

llvm-svn: 278269
This commit is contained in:
Andrew Kaylor 2016-08-10 18:56:35 +00:00
parent 592ddac7f2
commit 6ff0f9b54a
2 changed files with 89 additions and 2 deletions
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9
lib/Transforms/Scalar/IndVarSimplify.cpp
View File

@ -36,6 +36,7 @@
#include "llvm/Analysis/ScalarEvolutionAliasAnalysis.h"
#include "llvm/Analysis/TargetLibraryInfo.h"
#include "llvm/Analysis/TargetTransformInfo.h"
#include "llvm/Analysis/ValueTracking.h"
#include "llvm/IR/BasicBlock.h"
#include "llvm/IR/CFG.h"
#include "llvm/IR/Constants.h"
@ -1281,7 +1282,8 @@ Instruction *WidenIV::widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
}
}
// Our raison d'etre! Eliminate sign and zero extension.
if (IsSigned ? isa<SExtInst>(DU.NarrowUse) : isa<ZExtInst>(DU.NarrowUse)) {
if ((isa<SExtInst>(DU.NarrowUse) && (IsSigned || DU.NeverNegative)) ||
(isa<ZExtInst>(DU.NarrowUse) && (!IsSigned || DU.NeverNegative))) {
Value *NewDef = DU.WideDef;
if (DU.NarrowUse->getType() != WideType) {
unsigned CastWidth = SE->getTypeSizeInBits(DU.NarrowUse->getType());
@ -1370,9 +1372,12 @@ Instruction *WidenIV::widenIVUse(NarrowIVDefUse DU, SCEVExpander &Rewriter) {
///
void WidenIV::pushNarrowIVUsers(Instruction *NarrowDef, Instruction *WideDef) {
const SCEV *NarrowSCEV = SE->getSCEV(NarrowDef);
// isKnownPredicate is enough for most cases but still need isKnownNonNegative
// here to work around conservatism in ScalarEvolution about no-wrap flags.
bool NeverNegative =
SE->isKnownPredicate(ICmpInst::ICMP_SGE, NarrowSCEV,
SE->getConstant(NarrowSCEV->getType(), 0));
SE->getConstant(NarrowSCEV->getType(), 0)) ||
isKnownNonNegative(NarrowDef, NarrowDef->getModule()->getDataLayout());
for (User *U : NarrowDef->users()) {
Instruction *NarrowUser = cast<Instruction>(U);

82
test/Transforms/IndVarSimplify/iv-widen-elim-ext.ll Normal file
View File

@ -0,0 +1,82 @@
; RUN: opt < %s -indvars -S | FileCheck %s
target datalayout = "p:64:64:64-n32:64"
; When widening IV and its users, trunc and zext/sext are not needed
; if the original 32-bit user is known to be non-negative, whether
; the IV is considered signed or unsigned.
define void @foo(i32* %A, i32* %B, i32* %C, i32 %N) {
; CHECK-LABEL: @foo(
; CHECK-NOT: zext
; CHECK-NOT: sext
entry:
%cmp1 = icmp slt i32 0, %N
br i1 %cmp1, label %for.body.lr.ph, label %for.end
for.body.lr.ph: ; preds = %entry
br label %for.body
for.body: ; preds = %for.body.lr.ph, %for.inc
%i.02 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
%idxprom = sext i32 %i.02 to i64
%arrayidx = getelementptr inbounds i32, i32* %B, i64 %idxprom
%0 = load i32, i32* %arrayidx, align 4
%add = add nsw i32 %i.02, 2
%idxprom1 = zext i32 %add to i64
%arrayidx2 = getelementptr inbounds i32, i32* %C, i64 %idxprom1
%1 = load i32, i32* %arrayidx2, align 4
%add3 = add nsw i32 %0, %1
%idxprom4 = zext i32 %i.02 to i64
%arrayidx5 = getelementptr inbounds i32, i32* %A, i64 %idxprom4
store i32 %add3, i32* %arrayidx5, align 4
br label %for.inc
for.inc: ; preds = %for.body
%inc = add nsw i32 %i.02, 1
%cmp = icmp slt i32 %inc, %N
br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
for.cond.for.end_crit_edge: ; preds = %for.inc
br label %for.end
for.end: ; preds = %for.cond.for.end_crit_edge, %entry
ret void
}
define void @foo1(i32* %A, i32* %B, i32* %C, i32 %N) {
; CHECK-LABEL: @foo1(
; CHECK-NOT: zext
; CHECK-NOT: sext
entry:
%cmp1 = icmp slt i32 0, %N
br i1 %cmp1, label %for.body.lr.ph, label %for.end
for.body.lr.ph: ; preds = %entry
br label %for.body
for.body: ; preds = %for.body.lr.ph, %for.inc
%i.02 = phi i32 [ 0, %for.body.lr.ph ], [ %inc, %for.inc ]
%idxprom = zext i32 %i.02 to i64
%arrayidx = getelementptr inbounds i32, i32* %B, i64 %idxprom
%0 = load i32, i32* %arrayidx, align 4
%add = add nsw i32 %i.02, 2
%idxprom1 = sext i32 %add to i64
%arrayidx2 = getelementptr inbounds i32, i32* %C, i64 %idxprom1
%1 = load i32, i32* %arrayidx2, align 4
%add3 = add nsw i32 %0, %1
%idxprom4 = sext i32 %i.02 to i64
%arrayidx5 = getelementptr inbounds i32, i32* %A, i64 %idxprom4
store i32 %add3, i32* %arrayidx5, align 4
br label %for.inc
for.inc: ; preds = %for.body
%inc = add nsw i32 %i.02, 1
%cmp = icmp slt i32 %inc, %N
br i1 %cmp, label %for.body, label %for.cond.for.end_crit_edge
for.cond.for.end_crit_edge: ; preds = %for.inc
br label %for.end
for.end: ; preds = %for.cond.for.end_crit_edge, %entry
ret void
}