AMDGPU: Add basic folds for llvm.amdgcn.log

[foad]

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

457

Could use Src instead of creating a new poison?

[arsenm]

10717f92941d318b59bb6ac4c63f53723cf370d4

llvm/lib/Target/AMDGPU/AMDGPUInstCombineIntrinsic.cpp

case Intrinsic::amdgcn_rsq: {
     if (isa<UndefValue>(Src)) {
       Type *Ty = II.getType();
       auto *QNaN = ConstantFP::get(Ty, APFloat::getQNaN(Ty->getFltSemantics()));
       return IC.replaceInstUsesWith(II, QNaN);
     }
 
     break;
   }
+  case Intrinsic::amdgcn_log: {
+    Value *Src = II.getArgOperand(0);
+    Type *Ty = II.getType();
+
+    if (isa<PoisonValue>(Src))
+      return IC.replaceInstUsesWith(II, PoisonValue::get(Ty));
+
+    if (IC.getSimplifyQuery().isUndefValue(Src))
+      return IC.replaceInstUsesWith(II, ConstantFP::getNaN(Ty));
+
+    if (ConstantFP *C = dyn_cast<ConstantFP>(Src)) {
+      if (C->isInfinity() && !C->isNegative())
+        return IC.replaceInstUsesWith(II, C);
+
+      if (II.isStrictFP())
+        break;
+
+      if (C->isNaN()) {
+        Constant *Quieted = ConstantFP::get(Ty, C->getValue().makeQuiet());
+        return IC.replaceInstUsesWith(II, Quieted);
+      }
+
+      // f32 instruction doesn't handle denormals, f16 does.
+      if (C->isZero() || (C->getValue().isDenormal() && Ty->isFloatTy()))
+        return IC.replaceInstUsesWith(II, ConstantFP::getInfinity(Ty, true));
+
+      if (C->isNegative())
+        return IC.replaceInstUsesWith(II, ConstantFP::getNaN(Ty));
+
+      // TODO: Full constant folding matching hardware behavior.
+    }
+
+    break;
+  }
   case Intrinsic::amdgcn_frexp_mant:
   case Intrinsic::amdgcn_frexp_exp: {
     Value *Src = II.getArgOperand(0);
     if (const ConstantFP *C = dyn_cast<ConstantFP>(Src)) {
       int Exp;
       APFloat Significand =
           frexp(C->getValueAPF(), Exp, APFloat::rmNearestTiesToEven);
 

llvm/test/Transforms/InstCombine/AMDGPU/amdgcn-intrinsics.ll

 ; llvm.amdgcn.log
 ; --------------------------------------------------------------------
 
 declare float @llvm.amdgcn.log.f32(float) nounwind readnone
 declare half @llvm.amdgcn.log.f16(half) nounwind readnone
 
 define float @test_constant_fold_log_f32_undef() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_undef(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float undef)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF8000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float undef)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_poison() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_poison(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float poison)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float poison
 ;
   %val = call float @llvm.amdgcn.log.f32(float poison)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_p0() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_p0(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0.000000e+00)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0xFFF0000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0.0)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_n0() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_n0(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float -0.000000e+00)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0xFFF0000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float -0.0)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_subnormal() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_subnormal(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0x380FFFFFC0000000)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0xFFF0000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0x380FFFFFC0000000)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_negsubnormal() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_negsubnormal(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0xB80FFFFFC0000000)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0xFFF0000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0xB80FFFFFC0000000)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_pinf() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_pinf(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0x7FF0000000000000)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF0000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0x7FF0000000000000)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_ninf() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_ninf(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0xFFF0000000000000)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF8000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0xFFF0000000000000)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_p1() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_p1(
 ; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 1.000000e+00)

 ; CHECK-NEXT:    ret float [[VAL]]
 ;
   %val = call float @llvm.amdgcn.log.f32(float 10.0)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_neg10() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_neg10(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float -1.000000e+01)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF8000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float -10.0)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_qnan() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_qnan(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0x7FF8000000000000)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF8000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0x7FF8000000000000)
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_snan() {
 ; CHECK-LABEL: @test_constant_fold_log_f32_snan(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0x7FF0000020000000)
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF8000020000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0x7FF0000020000000)
   ret float %val
 }
 
 define half @test_constant_fold_log_f16_p0() {
 ; CHECK-LABEL: @test_constant_fold_log_f16_p0(
-; CHECK-NEXT:    [[VAL:%.*]] = call half @llvm.amdgcn.log.f16(half 0xH0000)
-; CHECK-NEXT:    ret half [[VAL]]
+; CHECK-NEXT:    ret half 0xHFC00
 ;
   %val = call half @llvm.amdgcn.log.f16(half 0.0)
   ret half %val
 }
 
 define half @test_constant_fold_log_f16_neg10() {
 ; CHECK-LABEL: @test_constant_fold_log_f16_neg10(
-; CHECK-NEXT:    [[VAL:%.*]] = call half @llvm.amdgcn.log.f16(half 0xHC900)
-; CHECK-NEXT:    ret half [[VAL]]
+; CHECK-NEXT:    ret half 0xH7E00
 ;
   %val = call half @llvm.amdgcn.log.f16(half -10.0)
   ret half %val
 }
 
 define float @test_constant_fold_log_f32_qnan_strictfp() strictfp {
 ; CHECK-LABEL: @test_constant_fold_log_f32_qnan_strictfp(
 ; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0x7FF8000000000000) #[[ATTR16]]

 ; CHECK-NEXT:    ret float [[VAL]]
 ;
   %val = call float @llvm.amdgcn.log.f32(float -10.0) strictfp
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_pinf_strictfp() strictfp {
 ; CHECK-LABEL: @test_constant_fold_log_f32_pinf_strictfp(
-; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0x7FF0000000000000) #[[ATTR16]]
-; CHECK-NEXT:    ret float [[VAL]]
+; CHECK-NEXT:    ret float 0x7FF0000000000000
 ;
   %val = call float @llvm.amdgcn.log.f32(float 0x7FF0000000000000) strictfp
   ret float %val
 }
 
 define float @test_constant_fold_log_f32_ninf_strictfp() strictfp {
 ; CHECK-LABEL: @test_constant_fold_log_f32_ninf_strictfp(
 ; CHECK-NEXT:    [[VAL:%.*]] = call float @llvm.amdgcn.log.f32(float 0xFFF0000000000000) #[[ATTR16]]

 ; CHECK-NEXT:    ret half [[VAL]]
 ;
   %val = call half @llvm.amdgcn.log.f16(half 0xH03ff)
   ret half %val
 }
 
 define half @test_constant_fold_log_f16_neg_denorm() {
 ; CHECK-LABEL: @test_constant_fold_log_f16_neg_denorm(
-; CHECK-NEXT:    [[VAL:%.*]] = call half @llvm.amdgcn.log.f16(half 0xH83FF)
-; CHECK-NEXT:    ret half [[VAL]]
+; CHECK-NEXT:    ret half 0xH7E00
 ;
   %val = call half @llvm.amdgcn.log.f16(half 0xH83ff)
   ret half %val
 }