[InstSimplify] fold select (fcmp X, Y), X, Y
This is NFCI for InstCombine because it calls InstSimplify,
so I left the tests for this transform there. As noted in
the code comment, we can allow this fold more often by using
FMF and/or value tracking.
llvm-svn: 346169
diff --git a/llvm/lib/Analysis/InstructionSimplify.cpp b/llvm/lib/Analysis/InstructionSimplify.cpp
index db929aa..fd6f4ba 100644
--- a/llvm/lib/Analysis/InstructionSimplify.cpp
+++ b/llvm/lib/Analysis/InstructionSimplify.cpp
@@ -3874,6 +3874,34 @@
return nullptr;
}
+/// Try to simplify a select instruction when its condition operand is a
+/// floating-point comparison.
+static Value *simplifySelectWithFCmp(Value *Cond, Value *T, Value *F) {
+ FCmpInst::Predicate Pred;
+ if (!match(Cond, m_FCmp(Pred, m_Specific(T), m_Specific(F))) &&
+ !match(Cond, m_FCmp(Pred, m_Specific(F), m_Specific(T))))
+ return nullptr;
+
+ // TODO: The transform may not be valid with -0.0. An incomplete way of
+ // testing for that possibility is to check if at least one operand is a
+ // non-zero constant.
+ const APFloat *C;
+ if ((match(T, m_APFloat(C)) && C->isNonZero()) ||
+ (match(F, m_APFloat(C)) && C->isNonZero())) {
+ // (T == F) ? T : F --> F
+ // (F == T) ? T : F --> F
+ if (Pred == FCmpInst::FCMP_OEQ)
+ return F;
+
+ // (T != F) ? T : F --> T
+ // (F != T) ? T : F --> T
+ if (Pred == FCmpInst::FCMP_UNE)
+ return T;
+ }
+
+ return nullptr;
+}
+
/// Given operands for a SelectInst, see if we can fold the result.
/// If not, this returns null.
static Value *SimplifySelectInst(Value *Cond, Value *TrueVal, Value *FalseVal,
@@ -3910,6 +3938,9 @@
simplifySelectWithICmpCond(Cond, TrueVal, FalseVal, Q, MaxRecurse))
return V;
+ if (Value *V = simplifySelectWithFCmp(Cond, TrueVal, FalseVal))
+ return V;
+
if (Value *V = foldSelectWithBinaryOp(Cond, TrueVal, FalseVal))
return V;