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IR: Fold away compares between GV GEPs and GVs

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A GEP of a non-weak global variable will not be equivalent to another
non-weak global variable or a GEP of such a variable.

Differential Revision: http://reviews.llvm.org/D4238

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@212360 91177308-0d34-0410-b5e6-96231b3b80d8
This commit is contained in:
David Majnemer 2014-07-04 22:05:26 +00:00
parent 483d89bcd4
commit 76735fbd2e
5 changed files with 44 additions and 16 deletions
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29
lib/IR/ConstantFold.cpp
View File

@ -1334,6 +1334,15 @@ static FCmpInst::Predicate evaluateFCmpRelation(Constant *V1, Constant *V2) {
return FCmpInst::BAD_FCMP_PREDICATE;
}
static ICmpInst::Predicate areGlobalsPotentiallyEqual(const GlobalValue *GV1,
const GlobalValue *GV2) {
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV1) && !isa<GlobalAlias>(GV2))
if (!GV1->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
return ICmpInst::ICMP_NE;
return ICmpInst::BAD_ICMP_PREDICATE;
}
/// evaluateICmpRelation - This function determines if there is anything we can
/// decide about the two constants provided. This doesn't need to handle simple
/// things like integer comparisons, but should instead handle ConstantExprs
@ -1395,10 +1404,7 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
// constant (which, since the types must match, means that it's a
// ConstantPointerNull).
if (const GlobalValue *GV2 = dyn_cast<GlobalValue>(V2)) {
// Don't try to decide equality of aliases.
if (!isa<GlobalAlias>(GV) && !isa<GlobalAlias>(GV2))
if (!GV->hasExternalWeakLinkage() || !GV2->hasExternalWeakLinkage())
return ICmpInst::ICMP_NE;
return areGlobalsPotentiallyEqual(GV, GV2);
} else if (isa<BlockAddress>(V2)) {
return ICmpInst::ICMP_NE; // Globals never equal labels.
} else {
@ -1463,7 +1469,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
}
break;
case Instruction::GetElementPtr:
case Instruction::GetElementPtr: {
GEPOperator *CE1GEP = cast<GEPOperator>(CE1);
// Ok, since this is a getelementptr, we know that the constant has a
// pointer type. Check the various cases.
if (isa<ConstantPointerNull>(V2)) {
@ -1510,7 +1517,8 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
"Surprising getelementptr!");
return isSigned ? ICmpInst::ICMP_SGT : ICmpInst::ICMP_UGT;
} else {
// If they are different globals, we don't know what the value is.
if (CE1GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(GV, GV2);
return ICmpInst::BAD_ICMP_PREDICATE;
}
}
@ -1526,8 +1534,14 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
// By far the most common case to handle is when the base pointers are
// obviously to the same global.
if (isa<GlobalValue>(CE1Op0) && isa<GlobalValue>(CE2Op0)) {
if (CE1Op0 != CE2Op0) // Don't know relative ordering.
// Don't know relative ordering, but check for inequality.
if (CE1Op0 != CE2Op0) {
GEPOperator *CE2GEP = cast<GEPOperator>(CE2);
if (CE1GEP->hasAllZeroIndices() && CE2GEP->hasAllZeroIndices())
return areGlobalsPotentiallyEqual(cast<GlobalValue>(CE1Op0),
cast<GlobalValue>(CE2Op0));
return ICmpInst::BAD_ICMP_PREDICATE;
}
// Ok, we know that both getelementptr instructions are based on the
// same global. From this, we can precisely determine the relative
// ordering of the resultant pointers.
@ -1573,6 +1587,7 @@ static ICmpInst::Predicate evaluateICmpRelation(Constant *V1, Constant *V2,
}
}
}
}
default:
break;
}

17
test/Other/constant-fold-gep.ll
View File

@ -467,4 +467,21 @@ define i8* @same_addrspace() nounwind noinline {
; OPT: ret i8* getelementptr inbounds ([4 x i8]* @p0, i32 0, i32 2)
}
@gv1 = internal global i32 1
@gv2 = internal global [1 x i32] [ i32 2 ]
@gv3 = internal global [1 x i32] [ i32 2 ]
; Handled by TI-independent constant folder
define i1 @gv_gep_vs_gv() {
ret i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @gv2, i32 0, i32 0), i32* @gv1)
}
; PLAIN: gv_gep_vs_gv
; PLAIN: ret i1 false
define i1 @gv_gep_vs_gv_gep() {
ret i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @gv2, i32 0, i32 0), i32* getelementptr inbounds ([1 x i32]* @gv3, i32 0, i32 0))
}
; PLAIN: gv_gep_vs_gv_gep
; PLAIN: ret i1 false
; CHECK: attributes #0 = { nounwind }

4
test/Transforms/InstCombine/2010-03-03-ExtElim.ll
View File

@ -22,11 +22,11 @@ define i1 @PR6486() nounwind {
define i1 @PR16462_1() nounwind {
; CHECK-LABEL: @PR16462_1(
ret i1 icmp sgt (i32 sext (i16 trunc (i32 select (i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @a, i32 0, i32 0), i32* @d), i32 0, i32 1) to i16) to i32), i32 65535)
; CHECK: ret i1 icmp sgt (i32 sext (i16 trunc (i32 select (i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @a, i32 0, i32 0), i32* @d), i32 0, i32 1) to i16) to i32), i32 65535)
; CHECK: ret i1 false
}
define i1 @PR16462_2() nounwind {
; CHECK-LABEL: @PR16462_2(
ret i1 icmp sgt (i32 sext (i16 trunc (i32 select (i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @a, i32 0, i32 0), i32* @d), i32 0, i32 1) to i16) to i32), i32 42)
; CHECK: ret i1 icmp sgt (i16 trunc (i32 select (i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @a, i32 0, i32 0), i32* @d), i32 0, i32 1) to i16), i16 42)
; CHECK: ret i1 false
}

8
test/Transforms/InstCombine/pr20079.ll
View File

@ -3,11 +3,7 @@
@c = internal global i32 0, align 4
; CHECK-LABEL: @fn1
; CHECK: [[ADD:%.*]] = add i32 %a, -1
; CHECK-NEXT: [[AND:%.*]] = and i32 [[ADD]], sub (i32 0, i32 zext (i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @b, i64 0, i64 0), i32* @c) to i32))
; CHECK-NEXT: ret i32 [[AND]]
; CHECK-NEXT: ret i32 0
define i32 @fn1(i32 %a) {
%xor = add i32 %a, -1
%mul = mul nsw i32 %xor, zext (i1 icmp eq (i32* getelementptr inbounds ([1 x i32]* @b, i64 0, i64 0), i32* @c) to i32)
ret i32 %mul
ret i32 0
}

2
test/Transforms/LoopVectorize/if-conversion.ll
View File

@ -156,7 +156,7 @@ for.body:
br i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 0), i32** @c), label %cond.false, label %cond.end
cond.false:
%cond.1 = or i32 %inc3, sdiv (i32 1, i32 zext (i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 0), i32** @c) to i32))
%cond.1 = or i32 %inc3, sdiv (i32 1, i32 zext (i1 icmp eq (i32** getelementptr inbounds ([1 x i32*]* @a, i64 0, i64 1), i32** @c) to i32))
br label %cond.end
cond.end: