[llvm] r254317 - [SimplifyLibCalls] Transform log(exp2(y)) to y*log(2) under fast-math.

[Davide Italiano via llvm-commits]

Author: davide
Date: Mon Nov 30 13:36:35 2015
New Revision: 254317

URL: http://llvm.org/viewvc/llvm-project?rev=254317&view=rev
Log:
[SimplifyLibCalls] Transform log(exp2(y)) to y*log(2) under fast-math.

Modified:
    llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
    llvm/trunk/test/Transforms/InstCombine/log-pow-nofastmath.ll
    llvm/trunk/test/Transforms/InstCombine/log-pow.ll

Modified: llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp?rev=254317&r1=254316&r2=254317&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp (original)
+++ llvm/trunk/lib/Transforms/Utils/SimplifyLibCalls.cpp Mon Nov 30 13:36:35 2015
@@ -1322,6 +1322,15 @@ Value *LibCallSimplifier::optimizeLog(Ca
     return B.CreateFMul(OpC->getArgOperand(1),
       EmitUnaryFloatFnCall(OpC->getOperand(0), Callee->getName(), B,
                            Callee->getAttributes()), "mul");
+
+  // log(exp2(y)) -> y*log(2)
+  if (F && Name == "log" && TLI->getLibFunc(F->getName(), Func) &&
+      TLI->has(Func) && Func == LibFunc::exp2)
+    return B.CreateFMul(
+        OpC->getArgOperand(0),
+        EmitUnaryFloatFnCall(ConstantFP::get(CI->getType(), 2.0),
+                             Callee->getName(), B, Callee->getAttributes()),
+        "logmul");
   return Ret;
 }
 
@@ -2301,7 +2310,6 @@ void LibCallSimplifier::replaceAllUsesWi
 // log, logf, logl:
 //   * log(exp(x))   -> x
 //   * log(exp(y))   -> y*log(e)
-//   * log(exp2(y))  -> y*log(2)
 //   * log(exp10(y)) -> y*log(10)
 //   * log(sqrt(x))  -> 0.5*log(x)
 //

Modified: llvm/trunk/test/Transforms/InstCombine/log-pow-nofastmath.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/log-pow-nofastmath.ll?rev=254317&r1=254316&r2=254317&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/log-pow-nofastmath.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/log-pow-nofastmath.ll Mon Nov 30 13:36:35 2015
@@ -13,5 +13,18 @@ entry:
 ; CHECK:   ret double %call
 ; CHECK: }
 
+define double @test3(double %x) #0 {
+  %call2 = call double @exp2(double %x) #0
+  %call3 = call double @log(double %call2) #0
+  ret double %call3
+}
+
+; CHECK-LABEL: @test3
+; CHECK:   %call2 = call double @exp2(double %x)
+; CHECK:   %call3 = call double @log(double %call2)
+; CHECK:   ret double %call3
+; CHECK: }
+
 declare double @log(double) #0
+declare double @exp2(double)
 declare double @llvm.pow.f64(double, double)

Modified: llvm/trunk/test/Transforms/InstCombine/log-pow.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/log-pow.ll?rev=254317&r1=254316&r2=254317&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/log-pow.ll (original)
+++ llvm/trunk/test/Transforms/InstCombine/log-pow.ll Mon Nov 30 13:36:35 2015
@@ -22,7 +22,20 @@ define double @test2(double ()* %fptr, d
 ; CHECK-LABEL: @test2
 ; CHECK: log
 
+define double @test3(double %x) #0 {
+  %call2 = call double @exp2(double %x) #0
+  %call3 = call double @log(double %call2) #0
+  ret double %call3
+}
+
+; CHECK-LABEL: @test3
+; CHECK:  %call2 = call double @exp2(double %x) #0
+; CHECK:  %logmul = fmul fast double %x, 0x3FE62E42FEFA39EF
+; CHECK:  ret double %logmul
+; CHECK: }
+
 declare double @log(double) #0
+declare double @exp2(double) #0
 declare double @llvm.pow.f64(double, double)
 
 attributes #0 = { "unsafe-fp-math"="true" }