[InstCombine] Remove hasOneUse check for pow(C,x) -> exp2(log2(C)*x)

[foad]

Summary

I don't think there's any good reason not to do this transformation when
the pow has multiple uses.

[lebedev.ri]

Seems reasonable.

[xbolva00]

Yeah

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

Value *LibCallSimplifier::replacePowWithExp(CallInst *Pow, IRBuilderBase &B) {
   // pow(10.0, x) -> exp10(x)
   // TODO: There is no exp10() intrinsic yet, but some day there shall be one.
   if (match(Base, m_SpecificFP(10.0)) &&
       hasFloatFn(TLI, Ty, LibFunc_exp10, LibFunc_exp10f, LibFunc_exp10l))
     return emitUnaryFloatFnCall(Expo, TLI, LibFunc_exp10, LibFunc_exp10f,
                                 LibFunc_exp10l, B, Attrs);
 
   // pow(n, x) -> exp2(log2(n) * x)
-  if (Pow->hasOneUse() && Pow->hasApproxFunc() && Pow->hasNoNaNs() &&
-      Pow->hasNoInfs() && BaseF->isNormal() && !BaseF->isNegative()) {
+  if (Pow->hasApproxFunc() && Pow->hasNoNaNs() && Pow->hasNoInfs() &&
+      BaseF->isNormal() && !BaseF->isNegative()) {
     Value *Log = nullptr;
     if (Ty->isFloatTy())
       Log = ConstantFP::get(Ty, std::log2(BaseF->convertToFloat()));
     else if (Ty->isDoubleTy())
       Log = ConstantFP::get(Ty, std::log2(BaseF->convertToDouble()));
 
     if (Log) {
       Value *FMul = B.CreateFMul(Log, Expo, "mul");

llvm/test/Transforms/InstCombine/pow-exp.ll

 ; CHECK-NEXT:    ret double [[CALL]]
 ;
   %call = tail call afn nnan ninf double @pow(double -4.000000e+00, double %e)
   ret double %call
 }
 
 define double @pow_multiuse(double %e) {
 ; CHECK-LABEL: @pow_multiuse(
-; CHECK-NEXT:    [[CALL:%.*]] = tail call nnan ninf afn double @pow(double 5.000000e+00, double [[E:%.*]])
-; CHECK-NEXT:    tail call void @use_d(double [[CALL]])
-; CHECK-NEXT:    ret double [[CALL]]
+; CHECK-NEXT:    [[MUL:%.*]] = fmul nnan ninf afn double [[E:%.*]], 0x4002934{{.*}}
+; CHECK-NEXT:    [[EXP2:%.*]] = call nnan ninf afn double @exp2(double [[MUL]])
+; CHECK-NEXT:    tail call void @use_d(double [[EXP2]])
+; CHECK-NEXT:    ret double [[EXP2]]
 ;
   %call = tail call afn nnan ninf double @pow(double 5.000000e+00, double %e)
   tail call void @use_d(double %call)
   ret double %call
 }
 
 define double @pow_ok_base_no_afn(double %e) {
 ; CHECK-LABEL: @pow_ok_base_no_afn(

 ; CHECK-NEXT:    ret float [[CALL]]
 ;
   %call = tail call afn nnan ninf float @powf(float -4.000000e+00, float %e)
   ret float %call
 }
 
 define float @powf_multiuse(float %e) {
 ; CHECK-LABEL: @powf_multiuse(
-; CHECK-NEXT:    [[CALL:%.*]] = tail call nnan ninf afn float @powf(float 5.000000e+00, float [[E:%.*]])
-; CHECK-NEXT:    tail call void @use_f(float [[CALL]])
-; CHECK-NEXT:    ret float [[CALL]]
+; CHECK-NEXT:    [[MUL:%.*]] = fmul nnan ninf afn float [[E:%.*]], 0x4002934{{.*}}
+; CHECK-NEXT:    [[EXP2F:%.*]] = call nnan ninf afn float @exp2f(float [[MUL]])
+; CHECK-NEXT:    tail call void @use_f(float [[EXP2F]])
+; CHECK-NEXT:    ret float [[EXP2F]]
 ;
   %call = tail call afn nnan ninf float @powf(float 5.000000e+00, float %e)
   tail call void @use_f(float %call)
   ret float %call
 }
 
 define float @powf_ok_base_no_afn(float %e) {
 ; CHECK-LABEL: @powf_ok_base_no_afn(