[SimplifyLibCalls] Add a new transformation: pow(exp(x), y) -> exp(x*y)

This one is enabled only under -ffast-math (due to rounding/overflows)
but allows us to emit shorter code.

Before (on FreeBSD x86-64):
4007f0:       50                      push   %rax
4007f1:       f2 0f 11 0c 24          movsd  %xmm1,(%rsp)
4007f6:       e8 75 fd ff ff          callq  400570 <exp2@plt>
4007fb:       f2 0f 10 0c 24          movsd  (%rsp),%xmm1
400800:       58                      pop    %rax
400801:       e9 7a fd ff ff          jmpq   400580 <pow@plt>
400806:       66 2e 0f 1f 84 00 00    nopw   %cs:0x0(%rax,%rax,1)
40080d:       00 00 00

After:
4007b0:       f2 0f 59 c1             mulsd  %xmm1,%xmm0
4007b4:       e9 87 fd ff ff          jmpq   400540 <exp2@plt>
4007b9:       0f 1f 80 00 00 00 00    nopl   0x0(%rax)

Differential Revision:	http://reviews.llvm.org/D14045

llvm-svn: 251976

3 files changed, 55 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/pow-exp-nofastmath.ll b/llvm/test/Transforms/InstCombine/pow-exp-nofastmath.ll
new file mode 100644
index 00000000000..9e596fa3a72
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pow-exp-nofastmath.ll
@@ -0,0 +1,17 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define double @mypow(double %x, double %y) #0 {
+entry:
+  %call = call double @exp(double %x)
+  %pow = call double @llvm.pow.f64(double %call, double %y)
+  ret double %pow
+}
+
+; CHECK-LABEL: define double @mypow(
+; CHECK:   %call = call double @exp(double %x)
+; CHECK:   %pow = call double @llvm.pow.f64(double %call, double %y)
+; CHECK:   ret double %pow
+; CHECK: }
+
+declare double @exp(double) #1
+declare double @llvm.pow.f64(double, double)
diff --git a/llvm/test/Transforms/InstCombine/pow-exp.ll b/llvm/test/Transforms/InstCombine/pow-exp.ll
new file mode 100644
index 00000000000..62e6fb4f3a3
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pow-exp.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define double @mypow(double %x, double %y) #0 {
+entry:
+  %call = call double @exp(double %x)
+  %pow = call double @llvm.pow.f64(double %call, double %y)
+  ret double %pow
+}
+
+; CHECK-LABEL: define double @mypow(
+; CHECK:   %mul = fmul fast double %x, %y
+; CHECK:   %exp = call double @exp(double %mul) #0
+; CHECK:   ret double %exp
+; CHECK: }
+
+declare double @exp(double) #1
+declare double @llvm.pow.f64(double, double)
+attributes #0 = { "unsafe-fp-math"="true" }
+attributes #1 = { "unsafe-fp-math"="true" }
diff --git a/llvm/test/Transforms/InstCombine/pow-exp2.ll b/llvm/test/Transforms/InstCombine/pow-exp2.ll
new file mode 100644
index 00000000000..ad7931c07a6
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/pow-exp2.ll
@@ -0,0 +1,19 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define double @mypow(double %x, double %y) #0 {
+entry:
+  %call = call double @exp2(double %x)
+  %pow = call double @llvm.pow.f64(double %call, double %y)
+  ret double %pow
+}
+
+; CHECK-LABEL: define double @mypow(
+; CHECK:   %mul = fmul fast double %x, %y
+; CHECK:   %exp2 = call double @exp2(double %mul) #0
+; CHECK:   ret double %exp2
+; CHECK: }
+
+declare double @exp2(double) #1
+declare double @llvm.pow.f64(double, double)
+attributes #0 = { "unsafe-fp-math"="true" }
+attributes #1 = { "unsafe-fp-math"="true" }