[SimplifyLibCalls] New transformation: tan(atan(x)) -> x

This is enabled only under -ffast-math.
So, instead of emitting:
  4007b0:       50                      push   %rax
  4007b1:       e8 8a fd ff ff          callq  400540 <atanf@plt>
  4007b6:       58                      pop    %rax
  4007b7:       e9 94 fd ff ff          jmpq   400550 <tanf@plt>
  4007bc:       0f 1f 40 00             nopl   0x0(%rax)

for:
float mytan(float x) {
  return tanf(atanf(x));
}
we emit a single retq.

Differential Revision:	 http://reviews.llvm.org/D14302

llvm-svn: 252098

2 files changed, 32 insertions, 0 deletions

diff --git a/llvm/test/Transforms/InstCombine/tan-nofastmath.ll b/llvm/test/Transforms/InstCombine/tan-nofastmath.ll
new file mode 100644
index 00000000000..0fe7b2c1d52
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/tan-nofastmath.ll
@@ -0,0 +1,17 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define float @mytan(float %x) {
+entry:
+  %call = call float @atanf(float %x)
+  %call1 = call float @tanf(float %call) 
+  ret float %call1
+}
+
+; CHECK-LABEL: define float @mytan(
+; CHECK:   %call = call float @atanf(float %x)
+; CHECK-NEXT:   %call1 = call float @tanf(float %call)
+; CHECK-NEXT:   ret float %call1
+; CHECK-NEXT: }
+
+declare float @tanf(float)
+declare float @atanf(float)
diff --git a/llvm/test/Transforms/InstCombine/tan.ll b/llvm/test/Transforms/InstCombine/tan.ll
new file mode 100644
index 00000000000..58e3bb355bd
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/tan.ll
@@ -0,0 +1,15 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+define float @mytan(float %x) #0 {
+entry:
+  %call = call float @atanf(float %x)
+  %call1 = call float @tanf(float %call)
+  ret float %call1
+}
+
+; CHECK-LABEL: define float @mytan(
+; CHECK:   ret float %x
+
+declare float @tanf(float) #0
+declare float @atanf(float) #0
+attributes #0 = { "unsafe-fp-math"="true" }