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The motivation is to recognize code such as this from /llvm/projects/test-suite/SingleSource/Benchmarks/BenchmarkGame/n-body.c: float distance = sqrt(dx * dx + dy * dy + dz * dz); float mag = dt / (distance * distance * distance); Without this patch, we don't match the sqrt as a reciprocal sqrt, so for PPC the new testcase in this patch produces: addis 3, 2, .LCPI4_2@toc@ha lfs 4, .LCPI4_2@toc@l(3) addis 3, 2, .LCPI4_1@toc@ha lfs 0, .LCPI4_1@toc@l(3) fcmpu 0, 1, 4 beq 0, .LBB4_2 # BB#1: frsqrtes 4, 1 addis 3, 2, .LCPI4_0@toc@ha lfs 5, .LCPI4_0@toc@l(3) fnmsubs 13, 1, 5, 1 fmuls 6, 4, 4 fmadds 1, 13, 6, 5 fmuls 1, 4, 1 fres 4, 1 <--- reciprocal of reciprocal square root fnmsubs 1, 1, 4, 0 fmadds 4, 4, 1, 4 .LBB4_2: fmuls 1, 4, 2 fres 2, 1 fnmsubs 0, 1, 2, 0 fmadds 0, 2, 0, 2 fmuls 1, 3, 0 blr After the patch, this simplifies to: frsqrtes 0, 1 addis 3, 2, .LCPI4_1@toc@ha fres 5, 2 lfs 4, .LCPI4_1@toc@l(3) addis 3, 2, .LCPI4_0@toc@ha lfs 7, .LCPI4_0@toc@l(3) fnmsubs 13, 1, 4, 1 fmuls 6, 0, 0 fnmsubs 2, 2, 5, 7 fmadds 1, 13, 6, 4 fmadds 2, 5, 2, 5 fmuls 0, 0, 1 fmuls 0, 0, 2 fmuls 1, 3, 0 blr Differential Revision: http://reviews.llvm.org/D5628 git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@219139 91177308-0d34-0410-b5e6-96231b3b80d8
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