[llvm-branch-commits] [llvm] a7176f8 - [ConstantFold] Remove handling for icmp of bitcast

[Nikita Popov via llvm-branch-commits]

Author: Nikita Popov
Date: 2023-11-03T12:22:59+01:00
New Revision: a7176f8a25fc6930ee7fd0cfcde4d9a96010a5a8

URL: https://github.com/llvm/llvm-project/commit/a7176f8a25fc6930ee7fd0cfcde4d9a96010a5a8
DIFF: https://github.com/llvm/llvm-project/commit/a7176f8a25fc6930ee7fd0cfcde4d9a96010a5a8.diff

LOG: [ConstantFold] Remove handling for icmp of bitcast

This only handles the case where the bitcast result is an integer
or pointer, and the input is not FP. This means that the input
can only be a vector. However, converting a comparison of the
whole vector into an element-wise comparison is generally not
correct.

I assume that this code was originally intended to handle the case
where a pointer bitcast is compared to a null pointer, which is
no longer relevant with opaque pointers.

Given the complete lack of test coverage, and the risk of
miscompiles if this code actually did something, I'm opting to
remove it entirely.

Added: 
    

Modified: 
    llvm/lib/IR/ConstantFold.cpp

Removed: 
    


################################################################################
diff  --git a/llvm/lib/IR/ConstantFold.cpp b/llvm/lib/IR/ConstantFold.cpp
index a10796e6da99dca..a4df579406538a4 100644
--- a/llvm/lib/IR/ConstantFold.cpp
+++ b/llvm/lib/IR/ConstantFold.cpp
@@ -1243,20 +1243,6 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
     Constant *CE1Op0 = CE1->getOperand(0);
 
     switch (CE1->getOpcode()) {
-    case Instruction::BitCast:
-      // We can't evaluate floating point casts or truncations.
-      if (CE1Op0->getType()->isFPOrFPVectorTy())
-        break;
-
-      // If the cast is not actually changing bits, and the second operand is a
-      // null pointer, do the comparison with the pre-casted value.
-      if (V2->isNullValue() && CE1->getType()->isIntOrPtrTy()) {
-        return evaluateICmpRelation(CE1Op0,
-                                    Constant::getNullValue(CE1Op0->getType()),
-                                    isSigned);
-      }
-      break;
-
     case Instruction::GetElementPtr: {
       GEPOperator *CE1GEP = cast<GEPOperator>(CE1);
       // Ok, since this is a getelementptr, we know that the constant has a