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

@@ -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")

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 {