[llvm] [ConstantFold] Fold `log1p` and `log1pf` when the input parameter is a constant value. (PR #112113)

[via llvm-commits]

llvmbot wrote:


<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-llvm-transforms

@llvm/pr-subscribers-llvm-analysis

Author: None (c8ef)

<details>
<summary>Changes</summary>

This patch adds support for constant folding for the `log1p` and `log1pf` libc functions.

---
Full diff: https://github.com/llvm/llvm-project/pull/112113.diff


2 Files Affected:

- (modified) llvm/lib/Analysis/ConstantFolding.cpp (+7-1) 
- (added) llvm/test/Transforms/InstCombine/log1p.ll (+113) 


``````````diff
diff --git a/llvm/lib/Analysis/ConstantFolding.cpp b/llvm/lib/Analysis/ConstantFolding.cpp
index 102762dc7937c6..303e1ca320e045 100644
--- a/llvm/lib/Analysis/ConstantFolding.cpp
+++ b/llvm/lib/Analysis/ConstantFolding.cpp
@@ -1679,7 +1679,8 @@ bool llvm::canConstantFoldCallTo(const CallBase *Call, const Function *F) {
   case 'l':
     return Name == "log" || Name == "logf" || Name == "logl" ||
            Name == "log2" || Name == "log2f" || Name == "log10" ||
-           Name == "log10f" || Name == "logb" || Name == "logbf";
+           Name == "log10f" || Name == "logb" || Name == "logbf" ||
+           Name == "log1p" || Name == "log1pf";
   case 'n':
     return Name == "nearbyint" || Name == "nearbyintf";
   case 'p':
@@ -2394,6 +2395,11 @@ static Constant *ConstantFoldScalarCall1(StringRef Name,
       if (!APF.isZero() && TLI->has(Func))
         return ConstantFoldFP(logb, APF, Ty);
       break;
+    case LibFunc_log1p:
+    case LibFunc_log1pf:
+      if (APF > APFloat(APF.getSemantics(), "-1") && TLI->has(Func))
+        return ConstantFoldFP(log1p, APF, Ty);
+      break;
     case LibFunc_logl:
       return nullptr;
     case LibFunc_nearbyint:
diff --git a/llvm/test/Transforms/InstCombine/log1p.ll b/llvm/test/Transforms/InstCombine/log1p.ll
new file mode 100644
index 00000000000000..9e22c3f43fb7a2
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/log1p.ll
@@ -0,0 +1,113 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=instcombine -S | FileCheck %s
+
+define float @log1pf_const() {
+; CHECK-LABEL: define float @log1pf_const() {
+; CHECK-NEXT:    [[R:%.*]] = call float @log1pf(float 7.000000e+00)
+; CHECK-NEXT:    ret float 0x4000A2B240000000
+;
+  %r = call float @log1pf(float 7.000000e+00)
+  ret float %r
+}
+
+define double @log1p_const() {
+; CHECK-LABEL: define double @log1p_const() {
+; CHECK-NEXT:    [[R:%.*]] = call double @log1p(double 7.000000e+00)
+; CHECK-NEXT:    ret double 0x4000A2B23F3BAB73
+;
+  %r = call double @log1p(double 7.000000e+00)
+  ret double %r
+}
+
+define float @log1pf_minus_one() {
+; CHECK-LABEL: define float @log1pf_minus_one() {
+; CHECK-NEXT:    [[R:%.*]] = call float @log1pf(float -1.000000e+00)
+; CHECK-NEXT:    ret float [[R]]
+;
+  %r = call float @log1pf(float -1.000000e+00)
+  ret float %r
+}
+
+define double @log1p_minus_one() {
+; CHECK-LABEL: define double @log1p_minus_one() {
+; CHECK-NEXT:    [[R:%.*]] = call double @log1p(double -1.000000e+00)
+; CHECK-NEXT:    ret double [[R]]
+;
+  %r = call double @log1p(double -1.000000e+00)
+  ret double %r
+}
+
+define float @log1pf_zero() {
+; CHECK-LABEL: define float @log1pf_zero() {
+; CHECK-NEXT:    [[R:%.*]] = call float @log1pf(float 0.000000e+00)
+; CHECK-NEXT:    ret float 0.000000e+00
+;
+  %r = call float @log1pf(float 0.000000e+00)
+  ret float %r
+}
+
+define double @log1p_zero() {
+; CHECK-LABEL: define double @log1p_zero() {
+; CHECK-NEXT:    [[R:%.*]] = call double @log1p(double 0.000000e+00)
+; CHECK-NEXT:    ret double 0.000000e+00
+;
+  %r = call double @log1p(double 0.000000e+00)
+  ret double %r
+}
+
+define float @log1pf_inf() {
+; CHECK-LABEL: define float @log1pf_inf() {
+; CHECK-NEXT:    [[R:%.*]] = call float @log1pf(float 0x7FF0000000000000)
+; CHECK-NEXT:    ret float [[R]]
+;
+  %r = call float @log1pf(float 0x7FF0000000000000)
+  ret float %r
+}
+
+define double @log1p_inf() {
+; CHECK-LABEL: define double @log1p_inf() {
+; CHECK-NEXT:    [[R:%.*]] = call double @log1p(double 0x7FF0000000000000)
+; CHECK-NEXT:    ret double [[R]]
+;
+  %r = call double @log1p(double 0x7FF0000000000000)
+  ret double %r
+}
+
+define float @log1pf_nan() {
+; CHECK-LABEL: define float @log1pf_nan() {
+; CHECK-NEXT:    [[R:%.*]] = call float @log1pf(float 0x7FF8000000000000)
+; CHECK-NEXT:    ret float [[R]]
+;
+  %r = call float @log1pf(float 0x7FF8000000000000)
+  ret float %r
+}
+
+define double @log1p_nan() {
+; CHECK-LABEL: define double @log1p_nan() {
+; CHECK-NEXT:    [[R:%.*]] = call double @log1p(double 0x7FF8000000000000)
+; CHECK-NEXT:    ret double [[R]]
+;
+  %r = call double @log1p(double 0x7FF8000000000000)
+  ret double %r
+}
+
+define float @log1pf_poison() {
+; CHECK-LABEL: define float @log1pf_poison() {
+; CHECK-NEXT:    [[R:%.*]] = call float @log1pf(float poison)
+; CHECK-NEXT:    ret float [[R]]
+;
+  %r = call float @log1pf(float poison)
+  ret float %r
+}
+
+define double @log1p_poison() {
+; CHECK-LABEL: define double @log1p_poison() {
+; CHECK-NEXT:    [[R:%.*]] = call double @log1p(double poison)
+; CHECK-NEXT:    ret double [[R]]
+;
+  %r = call double @log1p(double poison)
+  ret double %r
+}
+
+declare float @log1pf(float)
+declare double @log1p(double)

``````````

</details>


https://github.com/llvm/llvm-project/pull/112113