a77346bad0
Up to now, the only way to set specified FMF flags in IRBuilder is to use `FastMathFlagGuard`. It makes the code ugly and hard to maintain. This patch introduces a helper class `FMFSource` to replace the original parameter `Instruction *FMFSource` in IRBuilder. To maximize the compatibility, it accepts an instruction or a specified FMF. This patch also removes the use of `FastMathFlagGuard` in some simple cases. Compile-time impact: https://llvm-compile-time-tracker.com/compare.php?from=f87a9db8322643ccbc324e317a75b55903129b55&to=9397e712f6010be15ccf62f12740e9b4a67de2f4&stat=instructions%3Au