[PATCH] D84942: [ConstantFolding] fold abs intrinsic

[Sanjay Patel via Phabricator via llvm-commits]

spatel created this revision.
spatel added reviewers: nikic, aqjune, lebedev.ri.
Herald added subscribers: hiraditya, mcrosier.
Herald added a project: LLVM.
spatel requested review of this revision.

The handling for minimum value is similar to cttz/ctlz with 0 just above this case.


https://reviews.llvm.org/D84942

Files:
  llvm/lib/Analysis/ConstantFolding.cpp
  llvm/test/Analysis/ConstantFolding/abs.ll


Index: llvm/test/Analysis/ConstantFolding/abs.ll
===================================================================
--- llvm/test/Analysis/ConstantFolding/abs.ll
+++ llvm/test/Analysis/ConstantFolding/abs.ll
@@ -6,8 +6,7 @@
 
 define i8 @undef_val_min_poison() {
 ; CHECK-LABEL: @undef_val_min_poison(
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.abs.i8(i8 undef, i1 true)
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 undef
 ;
   %r = call i8 @llvm.abs.i8(i8 undef, i1 true)
   ret i8 %r
@@ -15,8 +14,7 @@
 
 define i8 @undef_val_min_not_poison() {
 ; CHECK-LABEL: @undef_val_min_not_poison(
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.abs.i8(i8 undef, i1 false)
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 0
 ;
   %r = call i8 @llvm.abs.i8(i8 undef, i1 false)
   ret i8 %r
@@ -24,8 +22,7 @@
 
 define i8 @min_val_min_poison() {
 ; CHECK-LABEL: @min_val_min_poison(
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.abs.i8(i8 -128, i1 true)
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 undef
 ;
   %r = call i8 @llvm.abs.i8(i8 -128, i1 true)
   ret i8 %r
@@ -33,8 +30,7 @@
 
 define i8 @min_val_min_not_poison() {
 ; CHECK-LABEL: @min_val_min_not_poison(
-; CHECK-NEXT:    [[R:%.*]] = call i8 @llvm.abs.i8(i8 -128, i1 false)
-; CHECK-NEXT:    ret i8 [[R]]
+; CHECK-NEXT:    ret i8 -128
 ;
   %r = call i8 @llvm.abs.i8(i8 -128, i1 false)
   ret i8 %r
@@ -42,8 +38,7 @@
 
 define <8 x i8> @vec_const() {
 ; CHECK-LABEL: @vec_const(
-; CHECK-NEXT:    [[R:%.*]] = call <8 x i8> @llvm.abs.v8i8(<8 x i8> <i8 -127, i8 -126, i8 -42, i8 -1, i8 0, i8 1, i8 42, i8 127>, i1 true)
-; CHECK-NEXT:    ret <8 x i8> [[R]]
+; CHECK-NEXT:    ret <8 x i8> <i8 127, i8 126, i8 42, i8 1, i8 0, i8 1, i8 42, i8 127>
 ;
   %r = call <8 x i8> @llvm.abs.v8i8(<8 x i8> <i8 -127, i8 -126, i8 -42, i8 -1, i8 0, i8 1, i8 42, i8 127>, i1 1)
   ret <8 x i8> %r
Index: llvm/lib/Analysis/ConstantFolding.cpp
===================================================================
--- llvm/lib/Analysis/ConstantFolding.cpp
+++ llvm/lib/Analysis/ConstantFolding.cpp
@@ -1436,6 +1436,7 @@
   case Intrinsic::launder_invariant_group:
   case Intrinsic::strip_invariant_group:
   case Intrinsic::masked_load:
+  case Intrinsic::abs:
   case Intrinsic::smax:
   case Intrinsic::smin:
   case Intrinsic::umax:
@@ -2505,6 +2506,18 @@
         return ConstantInt::get(Ty, C0->countTrailingZeros());
       else
         return ConstantInt::get(Ty, C0->countLeadingZeros());
+
+    case Intrinsic::abs:
+      // Undef or minimum val operand with poison min --> undef
+      assert(C1 && "Must be constant int");
+      if (C1->isOneValue() && (!C0 || C0->isMinSignedValue()))
+        return UndefValue::get(Ty);
+
+      // Undef operand with no poison min --> 0 (sign bit must be clear)
+      if (C1->isNullValue() && !C0)
+        return Constant::getNullValue(Ty);
+
+      return ConstantInt::get(Ty, C0->abs());
     }
 
     return nullptr;


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