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Aggressively flip compare constant expressions where appropriate; constant 

folding in particular expects null to be on the RHS.

llvm-svn: 91587
This commit is contained in:
Eli Friedman 2009-12-17 06:07:04 +00:00
parent 3dfff974ec
commit e67cae33e1
2 changed files with 13 additions and 3 deletions
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8
llvm/lib/VMCore/ConstantFold.cpp
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@ -1839,14 +1839,16 @@ Constant *llvm::ConstantFoldCompareInstruction(LLVMContext &Context,
} }
} }
if (!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) { if ((!isa<ConstantExpr>(C1) && isa<ConstantExpr>(C2)) ||
(C1->isNullValue() && !C2->isNullValue())) {
// If C2 is a constant expr and C1 isn't, flip them around and fold the // If C2 is a constant expr and C1 isn't, flip them around and fold the
// other way if possible. // other way if possible.
// Also, if C1 is null and C2 isn't, flip them around.
switch (pred) { switch (pred) {
case ICmpInst::ICMP_EQ: case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE: case ICmpInst::ICMP_NE:
// No change of predicate required. // No change of predicate required.
return ConstantFoldCompareInstruction(Context, pred, C2, C1); return ConstantExpr::getICmp(pred, C2, C1);
case ICmpInst::ICMP_ULT: case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT: case ICmpInst::ICMP_SLT:
@ -1858,7 +1860,7 @@ Constant *llvm::ConstantFoldCompareInstruction(LLVMContext &Context,
case ICmpInst::ICMP_SGE: case ICmpInst::ICMP_SGE:
// Change the predicate as necessary to swap the operands. // Change the predicate as necessary to swap the operands.
pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred); pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
return ConstantFoldCompareInstruction(Context, pred, C2, C1); return ConstantExpr::getICmp(pred, C2, C1);
default: // These predicates cannot be flopped around. default: // These predicates cannot be flopped around.
break; break;

8
llvm/test/Transforms/InstCombine/constant-fold-compare.ll Normal file
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@ -0,0 +1,8 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:32:32-n8:16:32"
define i32 @a() nounwind readnone {
entry:
ret i32 zext (i1 icmp eq (i32 0, i32 ptrtoint (i32 ()* @a to i32)) to i32)
}
; CHECK: ret i32 0