[llvm] 258a0a3 - [ConstraintElimination] Use simplified constraint for == 0.

[Florian Hahn via llvm-commits]

Author: Florian Hahn
Date: 2022-01-27T13:31:23Z
New Revision: 258a0a3a551745e7250d7831e6b477e49708a08c

URL: https://github.com/llvm/llvm-project/commit/258a0a3a551745e7250d7831e6b477e49708a08c
DIFF: https://github.com/llvm/llvm-project/commit/258a0a3a551745e7250d7831e6b477e49708a08c.diff

LOG: [ConstraintElimination] Use simplified constraint for == 0.

When checking x == 0, checking x u<= 0 is sufficient and simpler than
x u>= 0 && x u<= 0.

https://alive2.llvm.org/ce/z/btM7d3

    ----------------------------------------
    define i1 @src(i4 %a) {
    %0:
      %c = icmp eq i4 %a, 0
      ret i1 %c
    }
    =>
    define i1 @tgt(i4 %a) {
    %0:
       %c = icmp ule i4 %a, 0
       ret i1 %c
    }
    Transformation seems to be correct!

Added: 
    

Modified: 
    llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
    llvm/test/Transforms/ConstraintElimination/ne.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
index 0c4d7c8ecb483..e108135d41a57 100644
--- a/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
+++ b/llvm/lib/Transforms/Scalar/ConstraintElimination.cpp
@@ -187,6 +187,10 @@ getConstraint(CmpInst::Predicate Pred, Value *Op0, Value *Op1,
                          Value2Index, NewIndices);
 
   if (Pred == CmpInst::ICMP_EQ) {
+    if (match(Op1, m_Zero()))
+      return getConstraint(CmpInst::ICMP_ULE, Op0, Op1, Value2Index,
+                           NewIndices);
+
     auto A =
         getConstraint(CmpInst::ICMP_UGE, Op0, Op1, Value2Index, NewIndices);
     auto B =

diff  --git a/llvm/test/Transforms/ConstraintElimination/ne.ll b/llvm/test/Transforms/ConstraintElimination/ne.ll
index 084c24ff84c8f..2f6a54b7441ac 100644
--- a/llvm/test/Transforms/ConstraintElimination/ne.ll
+++ b/llvm/test/Transforms/ConstraintElimination/ne.ll
@@ -56,7 +56,7 @@ define i1 @test_ne_eq_0(i8 %a, i8 %b) {
 ; CHECK-NEXT:    [[C_3:%.*]] = icmp eq i8 [[A]], [[B]]
 ; CHECK-NEXT:    [[RES_3:%.*]] = xor i1 [[RES_2]], [[C_3]]
 ; CHECK-NEXT:    [[C_4:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT:    [[RES_4:%.*]] = xor i1 [[RES_3]], [[C_4]]
+; CHECK-NEXT:    [[RES_4:%.*]] = xor i1 [[RES_3]], false
 ; CHECK-NEXT:    [[T_2:%.*]] = icmp ugt i8 [[A]], 0
 ; CHECK-NEXT:    [[RES_5:%.*]] = xor i1 [[RES_4]], true
 ; CHECK-NEXT:    [[T_3:%.*]] = icmp uge i8 [[A]], 1
@@ -75,7 +75,7 @@ define i1 @test_ne_eq_0(i8 %a, i8 %b) {
 ; CHECK-NEXT:    [[C_9:%.*]] = icmp eq i8 [[A]], [[B]]
 ; CHECK-NEXT:    [[RES_11:%.*]] = xor i1 [[RES_10]], [[C_9]]
 ; CHECK-NEXT:    [[C_10:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT:    [[RES_12:%.*]] = xor i1 [[RES_11]], [[C_10]]
+; CHECK-NEXT:    [[RES_12:%.*]] = xor i1 [[RES_11]], true
 ; CHECK-NEXT:    [[F_2:%.*]] = icmp ugt i8 [[A]], 0
 ; CHECK-NEXT:    [[RES_13:%.*]] = xor i1 [[RES_12]], false
 ; CHECK-NEXT:    [[F_3:%.*]] = icmp uge i8 [[A]], 1
@@ -221,7 +221,7 @@ define i1 @test_ne_eq_1(i8 %a, i8 %b) {
 ; CHECK-NEXT:    [[C_11:%.*]] = icmp eq i8 [[A]], [[B]]
 ; CHECK-NEXT:    [[RES_11:%.*]] = xor i1 [[RES_10]], [[C_11]]
 ; CHECK-NEXT:    [[F_1:%.*]] = icmp eq i8 [[A]], 0
-; CHECK-NEXT:    [[RES_12:%.*]] = xor i1 [[RES_11]], [[F_1]]
+; CHECK-NEXT:    [[RES_12:%.*]] = xor i1 [[RES_11]], false
 ; CHECK-NEXT:    [[T_3:%.*]] = icmp ugt i8 [[A]], 0
 ; CHECK-NEXT:    [[RES_13:%.*]] = xor i1 [[RES_12]], true
 ; CHECK-NEXT:    [[T_4:%.*]] = icmp uge i8 [[A]], 1