[PATCH] D79409: [InstCombine] Remove hasNoInfs check for pow(C, y) -> exp2(log2(C)*y)

[Jay Foad via Phabricator via llvm-commits]

foad created this revision.
foad added reviewers: xbolva00, spatel, efriedma, evandro.
Herald added subscribers: llvm-commits, hiraditya.
Herald added a project: LLVM.

We already check hasNoNaNs and that x is finite and strictly positive.
That only leaves the following special cases (taken from the Linux man
page for pow):

If the absolute value of x is less than 1, and y is negative infinity, the result is positive infinity.
If the absolute value of x is greater than 1, and y is negative infinity, the result is +0.
If the absolute value of x is less than 1, and y is positive infinity, the result is +0.
If the absolute value of x is greater than 1, and y is positive infinity, the result is positive infinity.

The transformation preserves all of these, so there is no need to limit
it to hasNoInfs.


Repository:
  rG LLVM Github Monorepo

https://reviews.llvm.org/D79409

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


Index: llvm/test/Transforms/InstCombine/pow-exp.ll
===================================================================
--- llvm/test/Transforms/InstCombine/pow-exp.ll
+++ llvm/test/Transforms/InstCombine/pow-exp.ll
@@ -379,8 +379,9 @@
 
 define double @pow_ok_base_no_ninf(double %e) {
 ; CHECK-LABEL: @pow_ok_base_no_ninf(
-; CHECK-NEXT:    [[CALL:%.*]] = tail call nnan afn double @pow(double 0x3FE6666666666666, double [[E:%.*]])
-; CHECK-NEXT:    ret double [[CALL]]
+; CHECK-NEXT:    [[MUL:%.*]] = fmul nnan afn double [[E:%.*]], 0xBFE0776{{.*}}
+; CHECK-NEXT:    [[EXP2:%.*]] = call nnan afn double @exp2(double [[MUL]])
+; CHECK-NEXT:    ret double [[EXP2]]
 ;
   %call = tail call afn nnan double @pow(double 0x3FE6666666666666, double %e)
   ret double %call
Index: llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
===================================================================
--- llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -1565,7 +1565,7 @@
 
   // pow(n, x) -> exp2(log2(n) * x)
   if (Pow->hasOneUse() && Pow->hasApproxFunc() && Pow->hasNoNaNs() &&
-      Pow->hasNoInfs() && BaseF->isNormal() && !BaseF->isNegative()) {
+      BaseF->isNormal() && !BaseF->isNegative()) {
     Value *Log = nullptr;
     if (Ty->isFloatTy())
       Log = ConstantFP::get(Ty, std::log2(BaseF->convertToFloat()));


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