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The heuristic used by DAGCombine to form FMAs checks that the FMUL has only one use, but this is overly-conservative on some systems. Specifically, if the FMA and the FADD have the same latency (and the FMA does not compete for resources with the FMUL any more than the FADD does), there is no need for the restriction, and furthermore, forming the FMA leaving the FMUL can still allow for higher overall throughput and decreased critical-path length. Here we add a new TLI callback, enableAggressiveFMAFusion, false by default, to elide the hasOneUse check. This is enabled for PowerPC by default, as most PowerPC systems will benefit. Patch by Olivier Sallenave, thanks! git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@218120 91177308-0d34-0410-b5e6-96231b3b80d8
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