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When forming an addrec out of a phi don't just look at the last computation and steal its flags for our own, there may be other computations in the middle. Check whether the LHS of the computation is the phi itself and then we know it's safe to steal the flags. Fixes PR22795.

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There's a missed optimization opportunity where we could look at the full chain of computation and take the intersection of the flags instead of only looking one instruction deep.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@232134 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2015-03-13 01:37:52 +00:00
parent c666f5df88
commit 011cb4d5bd
2 changed files with 70 additions and 6 deletions
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12
lib/Analysis/ScalarEvolution.cpp
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@ -3591,10 +3591,12 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
// If the increment doesn't overflow, then neither the addrec nor
// the post-increment will overflow.
if (const AddOperator *OBO = dyn_cast<AddOperator>(BEValueV)) {
if (OBO->hasNoUnsignedWrap())
Flags = setFlags(Flags, SCEV::FlagNUW);
if (OBO->hasNoSignedWrap())
Flags = setFlags(Flags, SCEV::FlagNSW);
if (OBO->getOperand(0) == PN) {
if (OBO->hasNoUnsignedWrap())
Flags = setFlags(Flags, SCEV::FlagNUW);
if (OBO->hasNoSignedWrap())
Flags = setFlags(Flags, SCEV::FlagNSW);
}
} else if (GEPOperator *GEP = dyn_cast<GEPOperator>(BEValueV)) {
// If the increment is an inbounds GEP, then we know the address
// space cannot be wrapped around. We cannot make any guarantee
@ -3602,7 +3604,7 @@ const SCEV *ScalarEvolution::createNodeForPHI(PHINode *PN) {
// unsigned but we may have a negative index from the base
// pointer. We can guarantee that no unsigned wrap occurs if the
// indices form a positive value.
if (GEP->isInBounds()) {
if (GEP->isInBounds() && GEP->getOperand(0) == PN) {
Flags = setFlags(Flags, SCEV::FlagNW);
const SCEV *Ptr = getSCEV(GEP->getPointerOperand());

64
test/Analysis/ScalarEvolution/trip-count.ll
View File

@ -1,11 +1,15 @@
; RUN: opt < %s -analyze -scalar-evolution -scalar-evolution-max-iterations=0 | FileCheck %s
; PR1101
target datalayout = "e-m:e-i64:64-f80:128-n8:16:32:64-S128"
target triple = "x86_64-unknown-linux-gnu"
@A = weak global [1000 x i32] zeroinitializer, align 32
; CHECK: Printing analysis 'Scalar Evolution Analysis' for function 'test1':
; CHECK: backedge-taken count is 10000
define void @test(i32 %N) {
define void @test1(i32 %N) {
entry:
br label %bb3
@ -26,3 +30,61 @@ bb5: ; preds = %bb3
return: ; preds = %bb5
ret void
}
; PR22795
; CHECK: Printing analysis 'Scalar Evolution Analysis' for function 'test2':
; CHECK: %iv = phi i32 [ -1, %entry ], [ %next.1, %for.inc.1 ]
; CHECK-NEXT: --> {-1,+,2}<%preheader> U: full-set S: full-set Exits: 13
define i32 @test2() {
entry:
%bins = alloca [16 x i64], align 16
%0 = bitcast [16 x i64]* %bins to i8*
call void @llvm.memset.p0i8.i64(i8* %0, i8 0, i64 128, i32 16, i1 false)
br label %preheader
preheader: ; preds = %for.inc.1, %entry
%v11 = phi i64 [ 0, %entry ], [ %next12.1, %for.inc.1 ]
%iv = phi i32 [ -1, %entry ], [ %next.1, %for.inc.1 ]
%cmp = icmp sgt i64 %v11, 0
br i1 %cmp, label %for.body, label %for.inc
for.body: ; preds = %preheader
%zext = zext i32 %iv to i64
%arrayidx = getelementptr [16 x i64], [16 x i64]* %bins, i64 0, i64 %v11
%loaded = load i64, i64* %arrayidx, align 8
%add = add i64 %loaded, 1
%add2 = add i64 %add, %zext
store i64 %add2, i64* %arrayidx, align 8
br label %for.inc
for.inc: ; preds = %for.body, %preheader
%next12 = add nuw nsw i64 %v11, 1
%next = add nsw i32 %iv, 1
br i1 true, label %for.body.1, label %for.inc.1
end: ; preds = %for.inc.1
%arrayidx8 = getelementptr [16 x i64], [16 x i64]* %bins, i64 0, i64 2
%load = load i64, i64* %arrayidx8, align 16
%shr4 = lshr i64 %load, 32
%conv = trunc i64 %shr4 to i32
ret i32 %conv
for.body.1: ; preds = %for.inc
%zext.1 = zext i32 %next to i64
%arrayidx.1 = getelementptr [16 x i64], [16 x i64]* %bins, i64 0, i64 %next12
%loaded.1 = load i64, i64* %arrayidx.1, align 8
%add.1 = add i64 %loaded.1, 1
%add2.1 = add i64 %add.1, %zext.1
store i64 %add2.1, i64* %arrayidx.1, align 8
br label %for.inc.1
for.inc.1: ; preds = %for.body.1, %for.inc
%next12.1 = add nuw nsw i64 %next12, 1
%next.1 = add nuw nsw i32 %next, 1
%exitcond.1 = icmp eq i64 %next12.1, 16
br i1 %exitcond.1, label %end, label %preheader
}
; Function Attrs: nounwind
declare void @llvm.memset.p0i8.i64(i8* nocapture, i8, i64, i32, i1) #0