InstSimplify: Handle exp10(log10(x)) -> x

[arsenm]

Summary

Copy from exp/exp2 case.

[kpn]

How do we know that x is >0?

But I see that we don't worry about this for the existing cases so LGTM.

[arsenm]

In D157894#4585957, @kpn wrote:

How do we know that x is >0?

But I see that we don't worry about this for the existing cases so LGTM.

I guess you can argue that reassoc grants ignoring it, but it probably should require nnan

[arsenm]

5dcd6669ffdd03ca0adae5eda747ef68ed188d24

llvm/lib/Analysis/InstructionSimplify.cpp

if (Q.CxtI->hasAllowReassoc() &&
       return X;
     break;
   case Intrinsic::exp2:
     // exp2(log2(x)) -> x
     if (Q.CxtI->hasAllowReassoc() &&
         match(Op0, m_Intrinsic<Intrinsic::log2>(m_Value(X))))
       return X;
     break;
+  case Intrinsic::exp10:
+    // exp10(log10(x)) -> x
+    if (Q.CxtI->hasAllowReassoc() &&
+        match(Op0, m_Intrinsic<Intrinsic::log10>(m_Value(X))))
+      return X;
+    break;
   case Intrinsic::log:
     // log(exp(x)) -> x
     if (Q.CxtI->hasAllowReassoc() &&
         match(Op0, m_Intrinsic<Intrinsic::exp>(m_Value(X))))
       return X;
     break;
   case Intrinsic::log2:
     // log2(exp2(x)) -> x

llvm/test/Transforms/InstSimplify/log-exp-intrinsic.ll

;
   %2 = call reassoc double @llvm.log10.f64(double %1)
   %3 = call double @llvm.exp10.f64(double %2)
   %4 = call reassoc double @llvm.log10.f64(double %3)
   ret double %4
 }
 
 define double @exp10_reassoc_log10_strict(double %a) {
 ; CHECK-LABEL: @exp10_reassoc_log10_strict(
-; CHECK-NEXT:    [[TMP1:%.*]] = call double @llvm.log10.f64(double [[A:%.*]])
-; CHECK-NEXT:    [[TMP2:%.*]] = call reassoc double @llvm.exp10.f64(double [[TMP1]])
-; CHECK-NEXT:    ret double [[TMP2]]
+; CHECK-NEXT:    ret double [[A:%.*]]
 ;
   %1 = call double @llvm.log10.f64(double %a)
   %2 = call reassoc double @llvm.exp10.f64(double %1)
   ret double %2
 }
 
 define double @exp10_strict_log10_reassoc(double %a) {
 ; CHECK-LABEL: @exp10_strict_log10_reassoc(
;
   %2 = call double @llvm.exp10.f64(double %1)
   %3 = call double @llvm.log10.f64(double %2)
   %4 = call double @llvm.exp10.f64(double %3)
   ret double %4
 }
 
 define double @exp10_log10_exp10_log10_reassoc(double %a) {
 ; CHECK-LABEL: @exp10_log10_exp10_log10_reassoc(
-; CHECK-NEXT:    [[TMP1:%.*]] = call double @llvm.log10.f64(double [[A:%.*]])
-; CHECK-NEXT:    [[TMP2:%.*]] = call reassoc double @llvm.exp10.f64(double [[TMP1]])
-; CHECK-NEXT:    [[TMP3:%.*]] = call double @llvm.log10.f64(double [[TMP2]])
-; CHECK-NEXT:    [[TMP4:%.*]] = call reassoc double @llvm.exp10.f64(double [[TMP3]])
-; CHECK-NEXT:    ret double [[TMP4]]
+; CHECK-NEXT:    ret double [[A:%.*]]
 ;
   %1 = call double @llvm.log10.f64(double %a)
   %2 = call reassoc double @llvm.exp10.f64(double %1)
   %3 = call double @llvm.log10.f64(double %2)
   %4 = call reassoc double @llvm.exp10.f64(double %3)
   ret double %4
 }