maxjhandsome
/
llvm-project
forked from OSchip/llvm-project
1
0
Fork 0
Code Issues Pull Requests Packages Releases Wiki Activity

[IndVars] Make the fix for PR26973 more obvious; NFCI 

llvm-svn: 263828
This commit is contained in:
Sanjoy Das 2016-03-18 20:37:11 +00:00
parent 60fb899f28
commit 74af78e3b0
1 changed files with 42 additions and 3 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

45
llvm/lib/Transforms/Utils/SimplifyIndVar.cpp
View File

@ -200,9 +200,48 @@ void SimplifyIndvar::eliminateIVComparison(ICmpInst *ICmp, Value *IVOperand) {
NewRHS =
ICmp->getOperand(S == InvariantRHS ? IVOperIdx : (1 - IVOperIdx));
for (Value *Incoming : cast<PHINode>(IVOperand)->incoming_values()) {
if (NewLHS && NewRHS)
break;
auto *PN = cast<PHINode>(IVOperand);
for (unsigned i = 0, e = PN->getNumIncomingValues();
i != e && (!NewLHS || !NewRHS);
++i) {
// If this is a value incoming from the backedge, then it cannot be a loop
// invariant value (since we know that IVOperand is an induction variable).
if (L->contains(PN->getIncomingBlock(i)))
continue;
// NB! This following assert does not fundamentally have to be true, but
// it is true today given how SCEV analyzes induction variables.
// Specifically, today SCEV will *not* recognize %iv as an induction
// variable in the following case:
//
// define void @f(i32 %k) {
// entry:
// br i1 undef, label %r, label %l
//
// l:
// %k.inc.l = add i32 %k, 1
// br label %loop
//
// r:
// %k.inc.r = add i32 %k, 1
// br label %loop
//
// loop:
// %iv = phi i32 [ %k.inc.l, %l ], [ %k.inc.r, %r ], [ %iv.inc, %loop ]
// %iv.inc = add i32 %iv, 1
// br label %loop
// }
//
// but if it starts to, at some point, then the assertion below will have
// to be changed to a runtime check.
Value *Incoming = PN->getIncomingValue(i);
#ifndef NDEBUG
if (auto *I = dyn_cast<Instruction>(Incoming))
assert(DT->dominates(I, ICmp) && "Should be a unique loop dominating value!");
#endif
const SCEV *IncomingS = SE->getSCEV(Incoming);