[PowerPC] Implement combineRepeatedFPDivisors

This does not matter on newer cores (where we can use reciprocal estimates in
fast-math mode anyway), but for older cores this allows us to generate better
fast-math code where we have multiple FDIVs with a common divisor.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@222710 91177308-0d34-0410-b5e6-96231b3b80d8

test/CodeGen/PowerPC/fdiv-combine.ll

@@ -0,0 +1,39 @@
+; RUN: llc -mcpu=ppc64 < %s | FileCheck %s
+target datalayout = "E-m:e-i64:64-n32:64"
+target triple = "powerpc64-unknown-linux-gnu"
+
+; Following test case checks:
+;   a / D; b / D; c / D;
+;                =>
+;   recip = 1.0 / D; a * recip; b * recip; c * recip;
+
+define void @three_fdiv_double(double %D, double %a, double %b, double %c) #0 {
+; CHECK-LABEL: three_fdiv_double:
+; CHECK: fdiv
+; CHECK-NEXT-NOT: fdiv
+; CHECK: fmul
+; CHECK: fmul
+; CHECK: fmul
+  %div = fdiv double %a, %D
+  %div1 = fdiv double %b, %D
+  %div2 = fdiv double %c, %D
+  tail call void @foo_3d(double %div, double %div1, double %div2)
+  ret void
+}
+
+define void @two_fdiv_double(double %D, double %a, double %b) #0 {
+; CHECK-LABEL: two_fdiv_double:
+; CHECK: fdiv
+; CHECK: fdiv
+; CHECK-NEXT-NOT: fmul
+  %div = fdiv double %a, %D
+  %div1 = fdiv double %b, %D
+  tail call void @foo_2d(double %div, double %div1)
+  ret void
+}
+
+declare void @foo_3d(double, double, double)
+declare void @foo_3_2xd(<2 x double>, <2 x double>, <2 x double>)
+declare void @foo_2d(double, double)
+
+attributes #0 = { "unsafe-fp-math"="true" }