[llvm] f6b87da - [InstCombine] Fold comparison of abs with int min

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2020-09-08T20:23:03+02:00
New Revision: f6b87da0c73fcf7f8f051151ce62d2e07a466a8e

URL: https://github.com/llvm/llvm-project/commit/f6b87da0c73fcf7f8f051151ce62d2e07a466a8e
DIFF: https://github.com/llvm/llvm-project/commit/f6b87da0c73fcf7f8f051151ce62d2e07a466a8e.diff

LOG: [InstCombine] Fold comparison of abs with int min

If the abs is poisoning, this is already folded to true/false.
For non-poisoning abs, we can convert this to a comparison with
the operand.

Added: 
    

Modified: 
    llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
    llvm/test/Transforms/InstCombine/abs-intrinsic.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
index 608017b6dca2..74e9525e8ed4 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
@@ -3090,9 +3090,10 @@ Instruction *InstCombinerImpl::foldICmpEqIntrinsicWithConstant(
   switch (II->getIntrinsicID()) {
   case Intrinsic::abs:
     // abs(A) == 0  ->  A == 0
-    if (C.isNullValue())
+    // abs(A) == INT_MIN  ->  A == INT_MIN
+    if (C.isNullValue() || C.isMinSignedValue())
       return new ICmpInst(Cmp.getPredicate(), II->getArgOperand(0),
-                          Constant::getNullValue(Ty));
+                          ConstantInt::get(Ty, C));
     break;
 
   case Intrinsic::bswap:

diff  --git a/llvm/test/Transforms/InstCombine/abs-intrinsic.ll b/llvm/test/Transforms/InstCombine/abs-intrinsic.ll
index d63b0a21f217..30e5a9ddab3c 100644
--- a/llvm/test/Transforms/InstCombine/abs-intrinsic.ll
+++ b/llvm/test/Transforms/InstCombine/abs-intrinsic.ll
@@ -275,8 +275,7 @@ define i1 @abs_ne_int_min_poison(i8 %x) {
 
 define i1 @abs_eq_int_min_nopoison(i8 %x) {
 ; CHECK-LABEL: @abs_eq_int_min_nopoison(
-; CHECK-NEXT:    [[ABS:%.*]] = call i8 @llvm.abs.i8(i8 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[ABS]], -128
+; CHECK-NEXT:    [[CMP:%.*]] = icmp eq i8 [[X:%.*]], -128
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = call i8 @llvm.abs.i8(i8 %x, i1 false)
@@ -286,8 +285,7 @@ define i1 @abs_eq_int_min_nopoison(i8 %x) {
 
 define i1 @abs_ne_int_min_nopoison(i8 %x) {
 ; CHECK-LABEL: @abs_ne_int_min_nopoison(
-; CHECK-NEXT:    [[ABS:%.*]] = call i8 @llvm.abs.i8(i8 [[X:%.*]], i1 false)
-; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[ABS]], -128
+; CHECK-NEXT:    [[CMP:%.*]] = icmp ne i8 [[X:%.*]], -128
 ; CHECK-NEXT:    ret i1 [[CMP]]
 ;
   %abs = call i8 @llvm.abs.i8(i8 %x, i1 false)