6502/llvm-6502
1
0
Fork 0
mirror of https://github.com/c64scene-ar/llvm-6502.git synced 2024-07-21 02:29:22 +00:00
Code Issues Projects Releases Wiki Activity

Optimize icmp of null and select of two constants even if the select has

Browse Source 
multiple uses.  (The construct in question was found in gcc.)



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@91675 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Eli Friedman 2009-12-18 08:22:35 +00:00
parent 400073d546
commit 97b087c778
2 changed files with 33 additions and 15 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

32
lib/Transforms/Scalar/InstructionCombining.cpp
View File

@ -6356,24 +6356,26 @@ Instruction *InstCombiner::visitICmpInst(ICmpInst &I) {
// comparison into the select arms, which will cause one to be
// constant folded and the select turned into a bitwise or.
Value *Op1 = 0, *Op2 = 0;
if (LHSI->hasOneUse()) {
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1))) {
// Fold the known value into the constant operand.
Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
// Insert a new ICmp of the other select operand.
Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2),
RHSC, I.getName());
} else if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2))) {
// Fold the known value into the constant operand.
Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
// Insert a new ICmp of the other select operand.
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(1)))
Op1 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
if (Constant *C = dyn_cast<Constant>(LHSI->getOperand(2)))
Op2 = ConstantExpr::getICmp(I.getPredicate(), C, RHSC);
// We only want to perform this transformation if it will not lead to
// additional code. This is true if either both sides of the select
// fold to a constant (in which case the icmp is replaced with a select
// which will usually simplify) or this is the only user of the
// select (in which case we are trading a select+icmp for a simpler
// select+icmp).
if ((Op1 && Op2) || (LHSI->hasOneUse() && (Op1 || Op2))) {
if (!Op1)
Op1 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(1),
RHSC, I.getName());
}
}
if (Op1)
if (!Op2)
Op2 = Builder->CreateICmp(I.getPredicate(), LHSI->getOperand(2),
RHSC, I.getName());
return SelectInst::Create(LHSI->getOperand(0), Op1, Op2);
}
break;
}
case Instruction::Call:

16
test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll Normal file
View File

@ -0,0 +1,16 @@
; RUN: opt < %s -instcombine -S | FileCheck %s
@.str254 = internal constant [2 x i8] c".\00"
@.str557 = internal constant [3 x i8] c"::\00"
define i8* @demangle_qualified(i32 %isfuncname) nounwind {
entry:
%tobool272 = icmp ne i32 %isfuncname, 0
%cond276 = select i1 %tobool272, i8* getelementptr inbounds ([2 x i8]* @.str254, i32 0, i32 0), i8* getelementptr inbounds ([3 x i8]* @.str557, i32 0, i32 0) ; <i8*> [#uses=4]
%cmp.i504 = icmp eq i8* %cond276, null
%rval = getelementptr i8* %cond276, i1 %cmp.i504
ret i8* %rval
}
; CHECK: %cond276 = select i1
; CHECK: ret i8* %cond276