[PATCH] D22104: [SimplifyLibCalls] pow(x, 0.5) -> fabs(sqrt(x)) (finite-only-mode)

[Davide Italiano via llvm-commits]

davide updated this revision to Diff 63120.
davide added a comment.

Like this or you meant something different?


http://reviews.llvm.org/D22104

Files:
  lib/Transforms/Utils/SimplifyLibCalls.cpp
  test/Transforms/InstCombine/pow-sqrt.ll

Index: test/Transforms/InstCombine/pow-sqrt.ll
===================================================================
--- test/Transforms/InstCombine/pow-sqrt.ll
+++ test/Transforms/InstCombine/pow-sqrt.ll
@@ -11,3 +11,14 @@
 
 declare double @llvm.pow.f64(double, double)
 
+; In finite-only mode, we can transform pow(x, 0.5) -> fabs(sqrt(x))
+
+define double @pow_finite(double %x) {
+  %pow = call nnan ninf double @llvm.pow.f64(double %x, double 5.000000e-01)
+  ret double %pow
+}
+
+; CHECK-LABEL: define double @pow_finite(
+; CHECK-NEXT:  %sqrt = call double @sqrt(double %x)
+; CHECK-NEXT:  %fabs = call double @fabs(double %sqrt)
+; CHECK-NEXT:  ret double %fabs
Index: lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1052,15 +1052,19 @@
                                   Callee->getAttributes());
     }
 
-    // Expand pow(x, 0.5) to (x == -infinity ? +infinity : fabs(sqrt(x))).
+    // In finite-only mode, pow(x, 0.5) -> fabs(sqrt(x))
+    Value *Sqrt = emitUnaryFloatFnCall(Op1, "sqrt", B, Callee->getAttributes());
+    Value *FAbs =
+        emitUnaryFloatFnCall(Sqrt, "fabs", B, Callee->getAttributes());
+    if (CI->hasNoNaNs() && CI->hasNoInfs())
+      return FAbs;
+
+    // Otherwise, expand pow(x, 0.5) to
+    //   (x == -infinity ? +infinity : fabs(sqrt(x))).
     // This is faster than calling pow, and still handles negative zero
     // and negative infinity correctly.
-    // TODO: In finite-only mode, this could be just fabs(sqrt(x)).
     Value *Inf = ConstantFP::getInfinity(CI->getType());
     Value *NegInf = ConstantFP::getInfinity(CI->getType(), true);
-    Value *Sqrt = emitUnaryFloatFnCall(Op1, "sqrt", B, Callee->getAttributes());
-    Value *FAbs =
-        emitUnaryFloatFnCall(Sqrt, "fabs", B, Callee->getAttributes());
     Value *FCmp = B.CreateFCmpOEQ(Op1, NegInf);
     Value *Sel = B.CreateSelect(FCmp, Inf, FAbs);
     return Sel;


-------------- next part --------------
A non-text attachment was scrubbed...
Name: D22104.63120.patch
Type: text/x-patch
Size: 2045 bytes
Desc: not available
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20160707/90e6aed7/attachment.bin>