Generalize isLoopGuardedByCond's checking to consider two
SCEVUnknowns with identical Instructions to be equal. This allows
it to analze cases such as the attached testcase, where the front-end
has cloned the loop controlling expression. Along with r73805, this
lets IndVarSimplify eliminate all the sign-extend casts in the
loop in the attached testcase.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@73807 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ScalarEvolution.cpp b/lib/Analysis/ScalarEvolution.cpp
index 465807e..5a7e1b6 100644
--- a/lib/Analysis/ScalarEvolution.cpp
+++ b/lib/Analysis/ScalarEvolution.cpp
@@ -3655,6 +3655,29 @@
return 0;
}
+/// HasSameValue - SCEV structural equivalence is usually sufficient for
+/// testing whether two expressions are equal, however for the purposes of
+/// looking for a condition guarding a loop, it can be useful to be a little
+/// more general, since a front-end may have replicated the controlling
+/// expression.
+///
+static bool HasSameValue(const SCEVHandle &A, const SCEVHandle &B) {
+ // Quick check to see if they are the same SCEV.
+ if (A == B) return true;
+
+ // Otherwise, if they're both SCEVUnknown, it's possible that they hold
+ // two different instructions with the same value. Check for this case.
+ if (const SCEVUnknown *AU = dyn_cast<SCEVUnknown>(A))
+ if (const SCEVUnknown *BU = dyn_cast<SCEVUnknown>(B))
+ if (const Instruction *AI = dyn_cast<Instruction>(AU->getValue()))
+ if (const Instruction *BI = dyn_cast<Instruction>(BU->getValue()))
+ if (AI->isIdenticalTo(BI))
+ return true;
+
+ // Otherwise assume they may have a different value.
+ return false;
+}
+
/// isLoopGuardedByCond - Test whether entry to the loop is protected by
/// a conditional between LHS and RHS. This is used to help avoid max
/// expressions in loop trip counts.
@@ -3755,9 +3778,10 @@
SCEVHandle PreCondLHSSCEV = getSCEV(PreCondLHS);
SCEVHandle PreCondRHSSCEV = getSCEV(PreCondRHS);
- if ((LHS == PreCondLHSSCEV && RHS == PreCondRHSSCEV) ||
- (LHS == getNotSCEV(PreCondRHSSCEV) &&
- RHS == getNotSCEV(PreCondLHSSCEV)))
+ if ((HasSameValue(LHS, PreCondLHSSCEV) &&
+ HasSameValue(RHS, PreCondRHSSCEV)) ||
+ (HasSameValue(LHS, getNotSCEV(PreCondRHSSCEV)) &&
+ HasSameValue(RHS, getNotSCEV(PreCondLHSSCEV))))
return true;
}