[PATCH] D98235: An extra sqrtf was produced because of transformations in optimizePow function

[Daniil Seredkin via Phabricator via llvm-commits]

vdsered created this revision.
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See: https://bugs.llvm.org/show_bug.cgi?id=47613

There was an extra sqrt call because shrinking emitted a new powf and at the same time optimizePow replaces the previous pow with sqrt and as the result we have two instructions that will be in worklist of InstCombie despite the fact that %powf is not used by anyone (it is alive because of errno).

As the result we have two instructions:
%powf = call fast float @powf(float %x, float 5.000000e-01)
%sqrt = call fast double @sqrt(double %dx)

%powf will be converted to %sqrtf on a later iteration.

As a quick fix for that I moved shrinking to the end of optimizePow so that pow is replaced with sqrt at first that allows not to emit a new shrunk powf.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D98235

Files:
  llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
  llvm/test/Transforms/InstCombine/pow-4.ll


Index: llvm/test/Transforms/InstCombine/pow-4.ll
===================================================================
--- llvm/test/Transforms/InstCombine/pow-4.ll
+++ llvm/test/Transforms/InstCombine/pow-4.ll
@@ -1,7 +1,6 @@
 ; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
 ; RUN: opt -instcombine -S < %s                        | FileCheck %s --check-prefixes=CHECK,SQRT
 ; RUN: opt -instcombine -S < %s -disable-builtin sqrt  | FileCheck %s --check-prefixes=CHECK,NOSQRT
-
 declare double @llvm.pow.f64(double, double)
 declare float @llvm.pow.f32(float, float)
 declare <2 x double> @llvm.pow.v2f64(<2 x double>, <2 x double>)
@@ -235,12 +234,10 @@
 }
 
 ; (float)pow((double)(float)x, 0.5)
-; FIXME: One call to `sqrtf` would suffice (PR47613).
 define float @shrink_pow_libcall_half(float %x) {
 ; SQRT-LABEL: @shrink_pow_libcall_half(
-; SQRT-NEXT:    [[SQRTF:%.*]] = call fast float @sqrtf(float [[X:%.*]])
-; SQRT-NEXT:    [[SQRTF1:%.*]] = call fast float @sqrtf(float [[X]])
-; SQRT-NEXT:    ret float [[SQRTF1]]
+; SQRT-NEXT:    [[SQRTF:%.*]] = call fast float @sqrtf(float [[X]])
+; SQRT-NEXT:    ret float [[SQRTF]]
 ;
 ; NOSQRT-LABEL: @shrink_pow_libcall_half(
 ; NOSQRT-NEXT:    [[SQRTF:%.*]] = call fast float @sqrtf(float [[X:%.*]])
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1711,13 +1711,6 @@
   // Propagate the math semantics from the call to any created instructions.
   IRBuilderBase::FastMathFlagGuard Guard(B);
   B.setFastMathFlags(Pow->getFastMathFlags());
-
-  // Shrink pow() to powf() if the arguments are single precision,
-  // unless the result is expected to be double precision.
-  if (UnsafeFPShrink && Name == TLI->getName(LibFunc_pow) &&
-      hasFloatVersion(Name))
-    Shrunk = optimizeBinaryDoubleFP(Pow, B, true);
-
   // Evaluate special cases related to the base.
 
   // pow(1.0, x) -> 1.0
@@ -1818,6 +1811,12 @@
       return createPowWithIntegerExponent(Base, ExpoI, M, B);
   }
 
+  // Shrink pow() to powf() if the arguments are single precision,
+  // unless the result is expected to be double precision.
+  if (UnsafeFPShrink && Name == TLI->getName(LibFunc_pow) &&
+      hasFloatVersion(Name))
+    Shrunk = optimizeBinaryDoubleFP(Pow, B, true);
+
   return Shrunk;
 }
 


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