move CannotBeNegativeZero to ValueTracking. Simplify some signbit comparisons.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@51864 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/Analysis/ValueTracking.cpp b/lib/Analysis/ValueTracking.cpp
index a35d625..2fe6090 100644
--- a/lib/Analysis/ValueTracking.cpp
+++ b/lib/Analysis/ValueTracking.cpp
@@ -707,3 +707,53 @@
// shifting. We don't want to return '64' as for an i32 "0".
return std::max(FirstAnswer, std::min(TyBits, Mask.countLeadingZeros()));
}
+
+/// CannotBeNegativeZero - Return true if we can prove that the specified FP
+/// value is never equal to -0.0.
+///
+/// NOTE: this function will need to be revisited when we support non-default
+/// rounding modes!
+///
+bool llvm::CannotBeNegativeZero(const Value *V, unsigned Depth) {
+ if (const ConstantFP *CFP = dyn_cast<ConstantFP>(V))
+ return !CFP->getValueAPF().isNegZero();
+
+ if (Depth == 6)
+ return 1; // Limit search depth.
+
+ const Instruction *I = dyn_cast<Instruction>(V);
+ if (I == 0) return false;
+
+ // (add x, 0.0) is guaranteed to return +0.0, not -0.0.
+ if (I->getOpcode() == Instruction::Add &&
+ isa<ConstantFP>(I->getOperand(1)) &&
+ cast<ConstantFP>(I->getOperand(1))->isNullValue())
+ return true;
+
+ // sitofp and uitofp turn into +0.0 for zero.
+ if (isa<SIToFPInst>(I) || isa<UIToFPInst>(I))
+ return true;
+
+ if (const IntrinsicInst *II = dyn_cast<IntrinsicInst>(I))
+ // sqrt(-0.0) = -0.0, no other negative results are possible.
+ if (II->getIntrinsicID() == Intrinsic::sqrt)
+ return CannotBeNegativeZero(II->getOperand(1), Depth+1);
+
+ if (const CallInst *CI = dyn_cast<CallInst>(I))
+ if (const Function *F = CI->getCalledFunction()) {
+ if (F->isDeclaration()) {
+ switch (F->getNameLen()) {
+ case 3: // abs(x) != -0.0
+ if (!strcmp(F->getNameStart(), "abs")) return true;
+ break;
+ case 4: // abs[lf](x) != -0.0
+ if (!strcmp(F->getNameStart(), "absf")) return true;
+ if (!strcmp(F->getNameStart(), "absl")) return true;
+ break;
+ }
+ }
+ }
+
+ return false;
+}
+