Summary: Support pragma FP_CONTRACT under strict FP.

Reviewers: craig.topper, andrew.w.kaylor, uweigand, RKSimon, LiuChen3

Subscribers: hiraditya, jdoerfert, cfe-commits, llvm-commits, LuoYuanke

Tags: #clang, #llvm

Differential Revision: https://reviews.llvm.org/D72820

Summary: X86 has instructions to calculate fma and fneg at the same time. But we combine the fneg and fma only when fneg is the source operand under strict FP.

Reviewers: craig.topper, andrew.w.kaylor, uweigand, RKSimon, LiuChen3

Subscribers: LuoYuanke, llvm-commits, cfe-commits, jdoerfert, hiraditya

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D72824

Previously we mutated the node and then converted it to a libcall. But this loses the chain information.

This patch keeps the chain, but unfortunately breaks tail call optimization as the functions involved in deciding if a node is in tail call position can't handle the chain. But correct ordering seems more important to be right.

Somehow the SystemZ tests improved. I looked at one of them and it seemed that we're handling the split vector elements in a different order and that made the copies work better.

Differential Revision: https://reviews.llvm.org/D70334