[llvm-commits] [llvm] r91675 - in /llvm/trunk: lib/Transforms/Scalar/InstructionCombining.cpp test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll
Eli Friedman
eli.friedman at gmail.com
Fri Dec 18 00:22:36 PST 2009
Author: efriedma
Date: Fri Dec 18 02:22:35 2009
New Revision: 91675
URL: http://llvm.org/viewvc/llvm-project?rev=91675&view=rev
Log:
Optimize icmp of null and select of two constants even if the select has
multiple uses. (The construct in question was found in gcc.)
Added:
llvm/trunk/test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll
Modified:
llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
Modified: llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp?rev=91675&r1=91674&r2=91675&view=diff
==============================================================================
--- llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp (original)
+++ llvm/trunk/lib/Transforms/Scalar/InstructionCombining.cpp Fri Dec 18 02:22:35 2009
@@ -6356,24 +6356,26 @@
// 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:
Added: llvm/trunk/test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll?rev=91675&view=auto
==============================================================================
--- llvm/trunk/test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll (added)
+++ llvm/trunk/test/Transforms/InstCombine/2009-12-17-CmpSelectNull.ll Fri Dec 18 02:22:35 2009
@@ -0,0 +1,16 @@
+; RUN: opt < %s -instcombine -S | FileCheck %s
+
+ at .str254 = internal constant [2 x i8] c".\00"
+ at .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
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