[PATCH] [InstCombine] Fix issue in the simplification of pow() with nested exp{,2}()
Fix the issue of duplicating the call to `exp{,2}()` when it's nested in
`pow()`, as exposed by rL340462.
Differential revision: https://reviews.llvm.org/D51194
llvm-svn: 340784
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index 28c726c..86a1a79 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1194,23 +1194,39 @@
// pow(exp(x), y) -> exp(x * y)
// pow(exp2(x), y) -> exp2(x * y)
- // Only with fully relaxed math semantics, since, besides rounding
- // differences, the transformation changes overflow and underflow behavior
- // quite dramatically.
- // For example:
+ // If exp{,2}() is used only once, it is better to fold two transcendental
+ // math functions into one. If used again, exp{,2}() would still have to be
+ // called with the original argument, then keep both original transcendental
+ // functions. However, this transformation is only safe with fully relaxed
+ // math semantics, since, besides rounding differences, it changes overflow
+ // and underflow behavior quite dramatically. For example:
// pow(exp(1000), 0.001) = pow(inf, 0.001) = inf
// Whereas:
// exp(1000 * 0.001) = exp(1)
// TODO: Loosen the requirement for fully relaxed math semantics.
// TODO: Handle exp10() when more targets have it available.
CallInst *BaseFn = dyn_cast<CallInst>(Base);
- if (BaseFn && BaseFn->isFast() && Pow->isFast()) {
+ if (BaseFn && BaseFn->hasOneUse() && BaseFn->isFast() && Pow->isFast()) {
LibFunc LibFn;
+
Function *CalleeFn = BaseFn->getCalledFunction();
if (CalleeFn && TLI->getLibFunc(CalleeFn->getName(), LibFn) &&
(LibFn == LibFunc_exp || LibFn == LibFunc_exp2) && TLI->has(LibFn)) {
+ Value *ExpFn;
+
+ // Create new exp{,2}() with the product as its argument.
Value *FMul = B.CreateFMul(BaseFn->getArgOperand(0), Expo, "mul");
- return emitUnaryFloatFnCall(FMul, CalleeFn->getName(), B, Attrs);
+ ExpFn = emitUnaryFloatFnCall(FMul, CalleeFn->getName(), B,
+ BaseFn->getAttributes());
+
+ // Since the new exp{,2}() is different from the original one, dead code
+ // elimination cannot be trusted to remove it, since it may have side
+ // effects (e.g., errno). When the only consumer for the original
+ // exp{,2}() is pow(), then it has to be explicitly erased.
+ BaseFn->replaceAllUsesWith(ExpFn);
+ BaseFn->eraseFromParent();
+
+ return ExpFn;
}
}