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Make the 'icmp pred trunc(ext(X)), CST --> icmp pred X, ext(trunc(CST))'

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transformation much more careful. Truncating binary '01' to '1' sounds like it's
safe until you realize that it switched from positive to negative under a signed
interpretation, and that depends on the icmp predicate.

Also a few miscellaneous cleanups.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97721 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
Nick Lewycky 2010-03-04 06:54:10 +00:00
parent e57898ce55
commit 5bf7f88ea2
2 changed files with 23 additions and 24 deletions
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29
lib/VMCore/ConstantFold.cpp
View File

@ -2070,7 +2070,7 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
if (ConstantExpr *CE2 = dyn_cast<ConstantExpr>(C2)) {
Constant *CE2Op0 = CE2->getOperand(0);
if (CE2->getOpcode() == Instruction::BitCast &&
CE2->getType()->isVectorTy()==CE2Op0->getType()->isVectorTy()) {
CE2->getType()->isVectorTy() == CE2Op0->getType()->isVectorTy()) {
Constant *Inverse = ConstantExpr::getBitCast(C1, CE2Op0->getType());
return ConstantExpr::getICmp(pred, Inverse, CE2Op0);
}
@ -2078,8 +2078,8 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
// If the left hand side is an extension, try eliminating it.
if (ConstantExpr *CE1 = dyn_cast<ConstantExpr>(C1)) {
if (CE1->getOpcode() == Instruction::SExt ||
CE1->getOpcode() == Instruction::ZExt) {
if ((CE1->getOpcode() == Instruction::SExt && ICmpInst::isSigned(pred)) ||
(CE1->getOpcode() == Instruction::ZExt && !ICmpInst::isSigned(pred))){
Constant *CE1Op0 = CE1->getOperand(0);
Constant *CE1Inverse = ConstantExpr::getTrunc(CE1, CE1Op0->getType());
if (CE1Inverse == CE1Op0) {
@ -2097,27 +2097,8 @@ Constant *llvm::ConstantFoldCompareInstruction(unsigned short pred,
// If C2 is a constant expr and C1 isn't, flip them around and fold the
// other way if possible.
// Also, if C1 is null and C2 isn't, flip them around.
switch (pred) {
case ICmpInst::ICMP_EQ:
case ICmpInst::ICMP_NE:
// No change of predicate required.
return ConstantExpr::getICmp(pred, C2, C1);
case ICmpInst::ICMP_ULT:
case ICmpInst::ICMP_SLT:
case ICmpInst::ICMP_UGT:
case ICmpInst::ICMP_SGT:
case ICmpInst::ICMP_ULE:
case ICmpInst::ICMP_SLE:
case ICmpInst::ICMP_UGE:
case ICmpInst::ICMP_SGE:
// Change the predicate as necessary to swap the operands.
pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
return ConstantExpr::getICmp(pred, C2, C1);
default: // These predicates cannot be flopped around.
break;
}
pred = ICmpInst::getSwappedPredicate((ICmpInst::Predicate)pred);
return ConstantExpr::getICmp(pred, C2, C1);
}
}
return 0;

18
test/Transforms/InstCombine/2010-03-03-ExtElim.ll Normal file
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@ -0,0 +1,18 @@
; RUN: opt -instcombine -S %s | FileCheck %s
; PR6486
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"
target triple = "i386-unknown-linux-gnu"
@g_92 = common global [2 x i32*] zeroinitializer, align 4 ; <[2 x i32*]*> [#uses=1]
@g_177 = constant i32** bitcast (i8* getelementptr (i8* bitcast ([2 x i32*]* @g_92 to i8*), i64 4) to i32**), align 4 ; <i32***> [#uses=1]
define i1 @test() nounwind {
; CHECK: @test
%tmp = load i32*** @g_177 ; <i32**> [#uses=1]
%cmp = icmp ne i32** null, %tmp ; <i1> [#uses=1]
%conv = zext i1 %cmp to i32 ; <i32> [#uses=1]
%cmp1 = icmp sle i32 0, %conv ; <i1> [#uses=1]
ret i1 %cmp1
; CHECK: ret i1 true
}