[SimplifyLibCalls] Constant fold scalbxx #114417

fawdlstty · 2024-10-31T15:40:49Z

This patch adds constant folding support for scalbxx.
Reference: https://en.cppreference.com/w/cpp/numeric/math/scalbn

part2 of #112631

llvmbot · 2024-10-31T15:41:26Z

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Author: Fawdlstty (fawdlstty)

Changes

This patch adds constant folding support for scalbxx.
Reference: https://en.cppreference.com/w/cpp/numeric/math/scalbn

part2 of #112631

Full diff: https://github.com/llvm/llvm-project/pull/114417.diff

3 Files Affected:

(modified) llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h (+1)
(modified) llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp (+43)
(added) llvm/test/Transforms/InstCombine/scalbn.ll (+85)

diff --git a/llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h b/llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
index 128502b99d9a37..93ab5f5974c189 100644
--- a/llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
+++ b/llvm/include/llvm/Transforms/Utils/SimplifyLibCalls.h
@@ -213,6 +213,7 @@ class LibCallSimplifier {
   Value *optimizeSymmetric(CallInst *CI, LibFunc Func, IRBuilderBase &B);
   Value *optimizeRemquo(CallInst *CI, IRBuilderBase &B);
   Value *optimizeFdim(CallInst *CI, IRBuilderBase &B);
+  Value *optimizeScalbn(CallInst *CI, IRBuilderBase &B);
   // Wrapper for all floating point library call optimizations
   Value *optimizeFloatingPointLibCall(CallInst *CI, LibFunc Func,
                                       IRBuilderBase &B);
diff --git a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
index d85e0d99466022..afa2196243b538 100644
--- a/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
+++ b/llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp
@@ -3157,6 +3157,42 @@ Value *LibCallSimplifier::optimizeFdim(CallInst *CI, IRBuilderBase &B) {
   return ConstantFP::get(CI->getType(), MaxVal);
 }
 
+Value *LibCallSimplifier::optimizeScalbn(CallInst *CI, IRBuilderBase &B) {
+  Value *Base = CI->getArgOperand(0);
+  Value *Expo = CI->getArgOperand(1);
+  // Function *Callee = CI->getCalledFunction();
+  // StringRef Name = Callee->getName();
+  Type *Ty = CI->getType();
+  Module *M = CI->getModule();
+  // bool AllowApprox = CI->hasApproxFunc();
+  // bool Ignored;
+
+  // Propagate the math semantics from the call to any created instructions.
+  IRBuilderBase::FastMathFlagGuard Guard(B);
+  B.setFastMathFlags(CI->getFastMathFlags());
+  // Evaluate special cases related to the base.
+
+  // Scalbn(0.0, exp) -> 0.0
+  if (match(Base, m_SpecificFP(0.0)))
+    return Base;
+
+  // Scalbn(arg, 0) -> arg
+  if (match(Expo, m_Zero()))
+    return Base;
+
+  // Scalbn(arg, 1) -> arg * 2.0
+  if (match(Expo, m_SpecificInt(1)))
+    return B.CreateFMul(Base, ConstantFP::get(Ty, 2.0), "mul");
+
+  // Scalbn(1.0, exp) -> FLT_RADIX ^ exp
+  auto pow = createPowWithIntegerExponent(ConstantFP::get(Ty, 2.0), Expo, M, B);
+  if (match(Base, m_SpecificFP(1.0)))
+    return pow;
+
+  // otherwise
+  return B.CreateFMul(Base, pow, "mul");
+}
+
 //===----------------------------------------------------------------------===//
 // Integer Library Call Optimizations
 //===----------------------------------------------------------------------===//
@@ -4105,6 +4141,13 @@ Value *LibCallSimplifier::optimizeFloatingPointLibCall(CallInst *CI,
   case LibFunc_remquof:
   case LibFunc_remquol:
     return optimizeRemquo(CI, Builder);
+  case LibFunc_scalbln:
+  case LibFunc_scalblnf:
+  case LibFunc_scalblnl:
+  case LibFunc_scalbn:
+  case LibFunc_scalbnf:
+  case LibFunc_scalbnl:
+    return optimizeScalbn(CI, Builder);
   case LibFunc_nan:
   case LibFunc_nanf:
   case LibFunc_nanl:
diff --git a/llvm/test/Transforms/InstCombine/scalbn.ll b/llvm/test/Transforms/InstCombine/scalbn.ll
new file mode 100644
index 00000000000000..4dccef967973cf
--- /dev/null
+++ b/llvm/test/Transforms/InstCombine/scalbn.ll
@@ -0,0 +1,85 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 2
+; RUN: opt -S -passes=instcombine < %s | FileCheck %s
+
+declare double @scalbln(double, i64)
+declare float @scalblnf(float, i64)
+declare x86_fp80 @scalblnl(x86_fp80, i64)
+declare double @scalbn(double, i32)
+declare float @scalbnf(float, i32)
+declare x86_fp80 @scalbnl(x86_fp80, i32)
+
+;---------------------------------------------------------------------
+; scalbn(scalbn(x, a), b) -> scalbn(x, a + b)
+;---------------------------------------------------------------------
+
+define double @scalbln_scalbln(double %x, i64 %a, i64 %b) {
+; CHECK-LABEL: define double @scalbln
+; CHECK-SAME: (double [[X:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[SCALBXX0:%.*]] = call double @scalbln(double [[X]], i64 [[A]])
+; CHECK-NEXT:    [[SCALBXX1:%.*]] = call double @scalbln(double [[SCALBXX0]], i64 [[B]])
+; CHECK-NEXT:    ret double [[SCALBXX1]]
+;
+  %scalbxx0 = call double @scalbln(double %x, i64 %a)
+  %scalbxx1 = call double @scalbln(double %scalbxx0, i64 %b)
+  ret double %scalbxx1
+}
+
+define float @scalblnf_scalblnf(float %x, i64 %a, i64 %b) {
+; CHECK-LABEL: define float @scalblnf
+; CHECK-SAME: (float [[X:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[SCALBXX0:%.*]] = call float @scalblnf(float [[X]], i64 [[A]])
+; CHECK-NEXT:    [[SCALBXX1:%.*]] = call float @scalblnf(float [[SCALBXX0]], i64 [[B]])
+; CHECK-NEXT:    ret float [[SCALBXX1]]
+;
+  %scalbxx0 = call float @scalblnf(float %x, i64 %a)
+  %scalbxx1 = call float @scalblnf(float %scalbxx0, i64 %b)
+  ret float %scalbxx1
+}
+
+define x86_fp80 @scalblnl_scalblnl(x86_fp80 %x, i64 %a, i64 %b) {
+; CHECK-LABEL: define x86_fp80 @scalblnl
+; CHECK-SAME: (x86_fp80 [[X:%.*]], i64 [[A:%.*]], i64 [[B:%.*]]) {
+; CHECK-NEXT:    [[SCALBXX0:%.*]] = call x86_fp80 @scalblnl(x86_fp80 [[X]], i64 [[A]])
+; CHECK-NEXT:    [[SCALBXX1:%.*]] = call x86_fp80 @scalblnl(x86_fp80 [[SCALBXX0]], i64 [[B]])
+; CHECK-NEXT:    ret x86_fp80 [[SCALBXX1]]
+;
+  %scalbxx0 = call x86_fp80 @scalblnl(x86_fp80 %x, i64 %a)
+  %scalbxx1 = call x86_fp80 @scalblnl(x86_fp80 %scalbxx0, i64 %b)
+  ret x86_fp80 %scalbxx1
+}
+
+define double @scalbn_scalbn(double %x, i32 %a, i32 %b) {
+; CHECK-LABEL: define double @scalbn
+; CHECK-SAME: (double [[X:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:    [[SCALBXX0:%.*]] = call double @scalbn(double [[X]], i32 [[A]])
+; CHECK-NEXT:    [[SCALBXX1:%.*]] = call double @scalbn(double [[SCALBXX0]], i32 [[B]])
+; CHECK-NEXT:    ret double [[SCALBXX1]]
+;
+  %scalbxx0 = call double @scalbn(double %x, i32 %a)
+  %scalbxx1 = call double @scalbn(double %scalbxx0, i32 %b)
+  ret double %scalbxx1
+}
+
+define float @scalbnf_scalbnf(float %x, i32 %a, i32 %b) {
+; CHECK-LABEL: define float @scalbnf
+; CHECK-SAME: (float [[X:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:    [[SCALBXX0:%.*]] = call float @scalbnf(float [[X]], i32 [[A]])
+; CHECK-NEXT:    [[SCALBXX1:%.*]] = call float @scalbnf(float [[SCALBXX0]], i32 [[B]])
+; CHECK-NEXT:    ret float [[SCALBXX1]]
+;
+  %scalbxx0 = call float @scalbnf(float %x, i32 %a)
+  %scalbxx1 = call float @scalbnf(float %scalbxx0, i32 %b)
+  ret float %scalbxx1
+}
+
+define x86_fp80 @scalbnl_scalbnl(x86_fp80 %x, i32 %a, i32 %b) {
+; CHECK-LABEL: define x86_fp80 @scalbnl
+; CHECK-SAME: (x86_fp80 [[X:%.*]], i32 [[A:%.*]], i32 [[B:%.*]]) {
+; CHECK-NEXT:    [[SCALBXX0:%.*]] = call x86_fp80 @scalbnl(x86_fp80 [[X]], i32 [[A]])
+; CHECK-NEXT:    [[SCALBXX1:%.*]] = call x86_fp80 @scalbnl(x86_fp80 [[SCALBXX0]], i32 [[B]])
+; CHECK-NEXT:    ret x86_fp80 [[SCALBXX1]]
+;
+  %scalbxx0 = call x86_fp80 @scalbnl(x86_fp80 %x, i32 %a)
+  %scalbxx1 = call x86_fp80 @scalbnl(x86_fp80 %scalbxx0, i32 %b)
+  ret x86_fp80 %scalbxx1
+}

arsenm

This is handled in the wrong place, and is much more complicated than necessary.

The natural place for this is in lib/Analysis/ConstantFolding.cpp. You also do not need to match all the special cases, you can just use APFloat::scalbn.

scalbn is really just an alias for ldexp anyway, so really we should just canonicalize these into the ldexp intrinsic

llvm/lib/Transforms/Utils/SimplifyLibCalls.cpp

github-actions · 2024-11-02T15:59:14Z

✅ With the latest revision this PR passed the C/C++ code formatter.

arsenm

In any foldable cases, you could just replace this with the ldexp intrinsic

llvm/lib/Analysis/ConstantFolding.cpp

llvm/test/Transforms/InstCombine/scalbn.ll

llvm/lib/Analysis/ConstantFolding.cpp

llvm/test/Transforms/InstCombine/scalbn.ll

llvm/lib/Analysis/ConstantFolding.cpp

llvm/test/Transforms/InstSimplify/scalbn.ll

arsenm

In all of the cases where you are permitted to do this fold, we could also just replace this with the ldexp intrinsic

arsenm · 2024-11-22T19:06:10Z

llvm/test/Transforms/InstSimplify/scalbn.ll

+;
+  %call = call double @scalbn(double 1.0, i32 -1)
+  ret %call
+}


Negative test on overflow when errno is set

arsenm · 2024-11-22T19:06:42Z

llvm/test/Transforms/InstSimplify/scalbn.ll

+;
+  %call = call double @scalbn(double 1.0, i32 -1)
+  ret %call
+}


Add a strictfp test

add optimize method & test

16ff892

llvmbot added the llvm:transforms label Oct 31, 2024

dtcxzyw requested a review from arsenm October 31, 2024 15:45

arsenm added the floating-point Floating-point math label Oct 31, 2024

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impl in Analysis/ConstantFolding.cpp

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llvmbot added llvm:ir llvm:analysis Includes value tracking, cost tables and constant folding labels Nov 2, 2024

remove unused codes

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fawdlstty added 8 commits November 3, 2024 00:09

fix format error

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a

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remove repeated item

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mov eval method

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use apfloat scalbn impl

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fawdlstty added 2 commits November 5, 2024 21:32

remove convert & fix test

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move test file

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fawdlstty added 2 commits November 20, 2024 22:16

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[SimplifyLibCalls] Constant fold scalbxx #114417

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