From 805fa97a0f5ff61624855da37d4881708fb8f0fb Mon Sep 17 00:00:00 2001
From: Chris Lattner <sabre@nondot.org>
Date: Sun, 22 May 2011 22:22:35 +0000
Subject: [PATCH] implement PR9315, constant folding exp2 in terms of pow
 (since hosts without C99 runtimes don't have exp2).

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@131872 91177308-0d34-0410-b5e6-96231b3b80d8
---
 lib/Analysis/ConstantFolding.cpp   | 8 +++++++-
 test/Transforms/ConstProp/calls.ll | 7 ++++++-
 2 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/lib/Analysis/ConstantFolding.cpp b/lib/Analysis/ConstantFolding.cpp
index 5de2b04e80d..08a6065b31a 100644
--- a/lib/Analysis/ConstantFolding.cpp
+++ b/lib/Analysis/ConstantFolding.cpp
@@ -1085,7 +1085,7 @@ llvm::canConstantFoldCallTo(const Function *F) {
   case 'c':
     return Name == "cos" || Name == "ceil" || Name == "cosf" || Name == "cosh";
   case 'e':
-    return Name == "exp";
+    return Name == "exp" || Name == "exp2";
   case 'f':
     return Name == "fabs" || Name == "fmod" || Name == "floor";
   case 'l':
@@ -1221,6 +1221,12 @@ llvm::ConstantFoldCall(Function *F,
       case 'e':
         if (Name == "exp")
           return ConstantFoldFP(exp, V, Ty);
+  
+        if (Name == "exp2") {
+          // Constant fold exp2(x) as pow(2,x) in case the host doesn't have a
+          // C99 library.
+          return ConstantFoldBinaryFP(pow, 2.0, V, Ty);
+        }
         break;
       case 'f':
         if (Name == "fabs")
diff --git a/test/Transforms/ConstProp/calls.ll b/test/Transforms/ConstProp/calls.ll
index 82d73245ad1..3b6010a0dc3 100644
--- a/test/Transforms/ConstProp/calls.ll
+++ b/test/Transforms/ConstProp/calls.ll
@@ -7,6 +7,7 @@ declare double @sin(double)
 declare double @tan(double)
 
 declare double @sqrt(double)
+declare double @exp2(double)
 
 define double @T() {
 ; CHECK: @T
@@ -19,7 +20,11 @@ define double @T() {
   %b = fadd double %a, %C
   %D = call double @sqrt(double 4.000000e+00)
   %c = fadd double %b, %D
-  ret double %c
+
+  ; PR9315
+  %E = call double @exp2(double 4.0)
+  %d = fadd double %c, %E 
+  ret double %d
 }
 
 define i1 @test_sse_cvt() nounwind readnone {