[SCEV] Fix wrong Equal predicate created in getAddRecForPhiWithCasts
CreateAddRecFromPHIWithCastsImpl() adds an IncrementNUSW overflow predicate
which allows the PSCEV rewriter to rewrite this scev expression:
(zext i8 {0, + , (trunc i32 step to i8)} to i32)
into
{0, +, (sext i8 (trunc i32 step to i8) to i32)}
But then it adds the wrong Equal predicate:
%step == (zext i8 (trunc i32 %step to i8) to i32).
instead of:
%step == (sext i8 (trunc i32 %step to i8) to i32)
This is fixed here.
Differential Revision: https://reviews.llvm.org/D40641
llvm-svn: 320298
diff --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index 3ed7dde..960bd64 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -4636,18 +4636,19 @@
// Construct the extended SCEV: (Ext ix (Trunc iy (Expr) to ix) to iy)
// for each of StartVal and Accum
- auto GetExtendedExpr = [&](const SCEV *Expr) -> const SCEV * {
+ auto getExtendedExpr = [&](const SCEV *Expr,
+ bool CreateSignExtend) -> const SCEV * {
assert(isLoopInvariant(Expr, L) && "Expr is expected to be invariant");
const SCEV *TruncatedExpr = getTruncateExpr(Expr, TruncTy);
const SCEV *ExtendedExpr =
- Signed ? getSignExtendExpr(TruncatedExpr, Expr->getType())
- : getZeroExtendExpr(TruncatedExpr, Expr->getType());
+ CreateSignExtend ? getSignExtendExpr(TruncatedExpr, Expr->getType())
+ : getZeroExtendExpr(TruncatedExpr, Expr->getType());
return ExtendedExpr;
};
// Given:
// ExtendedExpr = (Ext ix (Trunc iy (Expr) to ix) to iy
- // = GetExtendedExpr(Expr)
+ // = getExtendedExpr(Expr)
// Determine whether the predicate P: Expr == ExtendedExpr
// is known to be false at compile time
auto PredIsKnownFalse = [&](const SCEV *Expr,
@@ -4656,13 +4657,15 @@
isKnownPredicate(ICmpInst::ICMP_NE, Expr, ExtendedExpr);
};
- const SCEV *StartExtended = GetExtendedExpr(StartVal);
+ const SCEV *StartExtended = getExtendedExpr(StartVal, Signed);
if (PredIsKnownFalse(StartVal, StartExtended)) {
DEBUG(dbgs() << "P2 is compile-time false\n";);
return None;
}
- const SCEV *AccumExtended = GetExtendedExpr(Accum);
+ // The Step is always Signed (because the overflow checks are either
+ // NSSW or NUSW)
+ const SCEV *AccumExtended = getExtendedExpr(Accum, /*CreateSignExtend=*/true);
if (PredIsKnownFalse(Accum, AccumExtended)) {
DEBUG(dbgs() << "P3 is compile-time false\n";);
return None;