[PATCH] Allow constant folding of round function

[Karthik Bhat]

Hi hfinkel,

Hi All,
This is another small patch which enables const folding a call to round whenever possible rounding it off to nearest decimal.
Could someone please review the same?
Thanks
Karthik Bhat

http://llvm-reviews.chandlerc.com/D2978

Files:
  test/Transforms/InstCombine/round.ll
  lib/Analysis/ConstantFolding.cpp

Index: test/Transforms/InstCombine/round.ll
===================================================================
--- test/Transforms/InstCombine/round.ll
+++ test/Transforms/InstCombine/round.ll
@@ -0,0 +1,90 @@
+; RUN: opt -S -instcombine < %s | FileCheck %s
+
+declare float @llvm.round.f32(float) #0
+declare double @llvm.round.f64(double) #0
+
+; CHECK-LABEL: @constant_fold_round_f32_01
+; CHECK-NEXT: ret float 1.000000e+00
+define float @constant_fold_round_f32_01() #0 {
+  %x = call float @llvm.round.f32(float 1.25) #0
+  ret float %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f32_02
+; CHECK-NEXT: ret float -1.000000e+00
+define float @constant_fold_round_f32_02() #0 {
+  %x = call float @llvm.round.f32(float -1.25) #0
+  ret float %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f32_03
+; CHECK-NEXT: ret float 2.000000e+00
+define float @constant_fold_round_f32_03() #0 {
+  %x = call float @llvm.round.f32(float 1.5) #0
+  ret float %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f32_04
+; CHECK-NEXT: ret float -2.000000e+00
+define float @constant_fold_round_f32_04() #0 {
+  %x = call float @llvm.round.f32(float -1.5) #0
+  ret float %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f32_05
+; CHECK-NEXT: ret float 3.000000e+00
+define float @constant_fold_round_f32_05() #0 {
+  %x = call float @llvm.round.f32(float 2.75) #0
+  ret float %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f32_06
+; CHECK-NEXT: ret float -3.000000e+00
+define float @constant_fold_round_f32_06() #0 {
+  %x = call float @llvm.round.f32(float -2.75) #0
+  ret float %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f64_01
+; CHECK-NEXT: ret double 1.000000e+00
+define double @constant_fold_round_f64_01() #0 {
+  %x = call double @llvm.round.f64(double 1.3) #0
+  ret double %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f64_02
+; CHECK-NEXT: ret double -1.000000e+00
+define double @constant_fold_round_f64_02() #0 {
+  %x = call double @llvm.round.f64(double -1.3) #0
+  ret double %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f64_03
+; CHECK-NEXT: ret double 2.000000e+00
+define double @constant_fold_round_f64_03() #0 {
+  %x = call double @llvm.round.f64(double 1.5) #0
+  ret double %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f64_04
+; CHECK-NEXT: ret double -2.000000e+00
+define double @constant_fold_round_f64_04() #0 {
+  %x = call double @llvm.round.f64(double -1.5) #0
+  ret double %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f64_05
+; CHECK-NEXT: ret double 3.000000e+00
+define double @constant_fold_round_f64_05() #0 {
+  %x = call double @llvm.round.f64(double 2.7) #0
+  ret double %x
+}
+
+; CHECK-LABEL: @constant_fold_round_f64_06
+; CHECK-NEXT: ret double -3.000000e+00
+define double @constant_fold_round_f64_06() #0 {
+  %x = call double @llvm.round.f64(double -2.7) #0
+  ret double %x
+}
+
+attributes #0 = { nounwind readnone }
Index: lib/Analysis/ConstantFolding.cpp
===================================================================
--- lib/Analysis/ConstantFolding.cpp
+++ lib/Analysis/ConstantFolding.cpp
@@ -1196,6 +1196,7 @@
   case Intrinsic::fma:
   case Intrinsic::fmuladd:
   case Intrinsic::copysign:
+  case Intrinsic::round:
   case Intrinsic::sadd_with_overflow:
   case Intrinsic::uadd_with_overflow:
   case Intrinsic::ssub_with_overflow:
@@ -1345,6 +1346,12 @@
       if (!Ty->isHalfTy() && !Ty->isFloatTy() && !Ty->isDoubleTy())
         return 0;
 
+      if (IntrinsicID == Intrinsic::round) {
+        APFloat V = Op->getValueAPF();
+        V.roundToIntegral(APFloat::rmNearestTiesToAway);
+        return ConstantFP::get(Ty->getContext(), V);
+      }
+
       /// We only fold functions with finite arguments. Folding NaN and inf is
       /// likely to be aborted with an exception anyway, and some host libms
       /// have known errors raising exceptions.
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