[llvm] 23de66d - [ConstFold] Don't fold signed comparison of gep of global

[Nikita Popov via llvm-commits]

Author: Nikita Popov
Date: 2021-12-28T14:13:33+01:00
New Revision: 23de66d1636b53ff4e52be91f6b84f014a6ae279

URL: https://github.com/llvm/llvm-project/commit/23de66d1636b53ff4e52be91f6b84f014a6ae279
DIFF: https://github.com/llvm/llvm-project/commit/23de66d1636b53ff4e52be91f6b84f014a6ae279.diff

LOG: [ConstFold] Don't fold signed comparison of gep of global

An inbounds GEP may still cross the sign boundary, so signed icmps
cannot be folded (https://alive2.llvm.org/ce/z/XSgi4D). This was
previously fixed for other folds in this function, but this one
was missed.

Added: 
    

Modified: 
    llvm/lib/IR/ConstantFold.cpp
    llvm/test/Assembler/ConstantExprFold.ll
    llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll

Removed: 
    


################################################################################
diff  --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index 8668fe82601c2..ae926f95cefe1 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1668,8 +1668,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
                  ++i, ++GTI)
               switch (IdxCompare(CE1->getOperand(i),
                                  CE2->getOperand(i), GTI.getIndexedType())) {
-              case -1: return isSigned ? ICmpInst::ICMP_SLT:ICmpInst::ICMP_ULT;
-              case 1:  return isSigned ? ICmpInst::ICMP_SGT:ICmpInst::ICMP_UGT;
+              case -1: return ICmpInst::ICMP_ULT;
+              case 1:  return ICmpInst::ICMP_UGT;
               case -2: return ICmpInst::BAD_ICMP_PREDICATE;
               }
 
@@ -1678,7 +1678,7 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
             for (; i < CE1->getNumOperands(); ++i)
               if (!CE1->getOperand(i)->isNullValue()) {
                 if (isa<ConstantInt>(CE1->getOperand(i)))
-                  return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
+                  return ICmpInst::ICMP_UGT;
                 else
                   return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal.
               }
@@ -1686,7 +1686,7 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
             for (; i < CE2->getNumOperands(); ++i)
               if (!CE2->getOperand(i)->isNullValue()) {
                 if (isa<ConstantInt>(CE2->getOperand(i)))
-                  return isSigned ? ICmpInst::ICMP_SLT : ICmpInst::ICMP_ULT;
+                  return ICmpInst::ICMP_ULT;
                 else
                   return ICmpInst::BAD_ICMP_PREDICATE; // Might be equal.
               }

diff  --git a/llvm/test/Assembler/ConstantExprFold.ll b/llvm/test/Assembler/ConstantExprFold.ll
index 96b3e54fcffed..523edd94bd05f 100644
--- a/llvm/test/Assembler/ConstantExprFold.ll
+++ b/llvm/test/Assembler/ConstantExprFold.ll
@@ -21,7 +21,7 @@
 
 @9 = global i1 icmp ult (i64* @A, i64* getelementptr (i64, i64* @A, i64 1))        ; true
 @10 = global i1 icmp slt (i64* @A, i64* getelementptr (i64, i64* @A, i64 0))        ; false
- at 11 = global i1 icmp slt (i32* getelementptr (%Ty, %Ty* @B, i64 0, i32 0),
+ at 11 = global i1 icmp ult (i32* getelementptr (%Ty, %Ty* @B, i64 0, i32 0),
                    i32* getelementptr (%Ty, %Ty* @B, i64 0, i32 1))            ; true
 ;global i1 icmp ne (i64* @A, i64* bitcast (%Ty* @B to i64*))                 ; true
 

diff  --git a/llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll b/llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll
index 9e5a54a8a65c1..ee33201a8a22e 100644
--- a/llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll
+++ b/llvm/test/Transforms/InstSimplify/ConstProp/icmp-global.ll
@@ -226,10 +226,10 @@ define i1 @global_gep_ugt_global_gep() {
   ret i1 %cmp
 }
 
-; TODO: Should not fold due to signed comparison.
+; Should not fold due to signed comparison.
 define i1 @global_gep_sgt_global_gep() {
 ; CHECK-LABEL: @global_gep_sgt_global_gep(
-; CHECK-NEXT:    ret i1 true
+; CHECK-NEXT:    ret i1 icmp sgt (i32* getelementptr inbounds ([2 x i32], [2 x i32]* @g, i64 0, i64 1), i32* getelementptr inbounds ([2 x i32], [2 x i32]* @g, i64 0, i64 0))
 ;
   %gep1 = getelementptr inbounds [2 x i32], [2 x i32]* @g, i64 0, i64 0
   %gep2 = getelementptr inbounds [2 x i32], [2 x i32]* @g, i64 0, i64 1