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[InstCombine] Make foldCmpLoadFromIndexedGlobal more resiliant to non-array geps. #150639

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Merged
merged 1 commit into from
Aug 3, 2025
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[InstCombine] Make foldCmpLoadFromIndexedGlobal more resiliant to non-array geps. #150639

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29 changes: 21 additions & 8 deletions llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -113,10 +113,16 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
LoadInst *LI, GetElementPtrInst *GEP, GlobalVariable *GV, CmpInst &ICI,
ConstantInt *AndCst) {
if (LI->isVolatile() || LI->getType() != GEP->getResultElementType() ||
GV->getValueType() != GEP->getSourceElementType() || !GV->isConstant() ||
!GV->getValueType()->isArrayTy() || !GV->isConstant() ||
!GV->hasDefinitiveInitializer())
return nullptr;

Type *GEPSrcEltTy = GEP->getSourceElementType();
if (GEPSrcEltTy->isArrayTy())
GEPSrcEltTy = GEPSrcEltTy->getArrayElementType();
if (GV->getValueType()->getArrayElementType() != GEPSrcEltTy)
return nullptr;

Constant *Init = GV->getInitializer();
if (!isa<ConstantArray>(Init) && !isa<ConstantDataArray>(Init))
return nullptr;
Expand All @@ -127,12 +133,19 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
return nullptr;

// There are many forms of this optimization we can handle, for now, just do
// the simple index into a single-dimensional array.
// the simple index into a single-dimensional array or elements of equal size.
//
// Require: GEP GV, 0, i {{, constant indices}}
if (GEP->getNumOperands() < 3 || !isa<ConstantInt>(GEP->getOperand(1)) ||
!cast<ConstantInt>(GEP->getOperand(1))->isZero() ||
isa<Constant>(GEP->getOperand(2)))
// Require: GEP [n x i8] GV, 0, Idx {{, constant indices}}
// Or: GEP i8 GV, Idx

unsigned GEPIdxOp = 1;
if (GEP->getSourceElementType()->isArrayTy()) {
GEPIdxOp = 2;
if (!match(GEP->getOperand(1), m_ZeroInt()))
return nullptr;
}
if (GEP->getNumOperands() < GEPIdxOp + 1 ||
isa<Constant>(GEP->getOperand(GEPIdxOp)))
return nullptr;

// Check that indices after the variable are constants and in-range for the
Expand All @@ -141,7 +154,7 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
SmallVector<unsigned, 4> LaterIndices;

Type *EltTy = Init->getType()->getArrayElementType();
for (unsigned i = 3, e = GEP->getNumOperands(); i != e; ++i) {
for (unsigned i = GEPIdxOp + 1, e = GEP->getNumOperands(); i != e; ++i) {
ConstantInt *Idx = dyn_cast<ConstantInt>(GEP->getOperand(i));
if (!Idx)
return nullptr; // Variable index.
Expand All @@ -163,7 +176,7 @@ Instruction *InstCombinerImpl::foldCmpLoadFromIndexedGlobal(
LaterIndices.push_back(IdxVal);
}

Value *Idx = GEP->getOperand(2);
Value *Idx = GEP->getOperand(GEPIdxOp);
// If the index type is non-canonical, wait for it to be canonicalized.
if (Idx->getType() != DL.getIndexType(GEP->getType()))
return nullptr;
Expand Down
32 changes: 31 additions & 1 deletion llvm/test/Transforms/InstCombine/load-cmp.ll
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Expand Up @@ -68,7 +68,6 @@ define i1 @test1_noinbounds_as1(i32 %x) {
%q = load i16, ptr addrspace(1) %p
%r = icmp eq i16 %q, 0
ret i1 %r

}

define i1 @test1_noinbounds_as2(i64 %x) {
Expand All @@ -81,7 +80,17 @@ define i1 @test1_noinbounds_as2(i64 %x) {
%q = load i16, ptr addrspace(2) %p
%r = icmp eq i16 %q, 0
ret i1 %r
}

define i1 @test1_noarrayty(i32 %X) {
; CHECK-LABEL: @test1_noarrayty(
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[X:%.*]], 9
; CHECK-NEXT: ret i1 [[R]]
;
%P = getelementptr inbounds i16, ptr @G16, i32 %X
%Q = load i16, ptr %P
%R = icmp eq i16 %Q, 0
ret i1 %R
}

define i1 @test2(i32 %X) {
Expand All @@ -104,7 +113,17 @@ define i1 @test3(i32 %X) {
%Q = load double, ptr %P
%R = fcmp oeq double %Q, 1.0
ret i1 %R
}

define i1 @test3_noarrayty(i32 %X) {
; CHECK-LABEL: @test3_noarrayty(
; CHECK-NEXT: [[R:%.*]] = icmp eq i32 [[X:%.*]], 1
; CHECK-NEXT: ret i1 [[R]]
;
%P = getelementptr inbounds double, ptr @GD, i32 %X
%Q = load double, ptr %P
%R = fcmp oeq double %Q, 1.0
ret i1 %R
}

define i1 @test4(i32 %X) {
Expand Down Expand Up @@ -326,6 +345,17 @@ define i1 @test10_struct_arr_noinbounds_i64(i64 %x) {
ret i1 %r
}

define i1 @test10_struct_arr_noarrayty(i32 %x) {
; CHECK-LABEL: @test10_struct_arr_noarrayty(
; CHECK-NEXT: [[R:%.*]] = icmp ne i32 [[X:%.*]], 1
; CHECK-NEXT: ret i1 [[R]]
;
%p = getelementptr inbounds %Foo, ptr @GStructArr, i32 %x, i32 2
%q = load i32, ptr %p
%r = icmp eq i32 %q, 9
ret i1 %r
}

@table = internal constant [2 x ptr] [ptr @g, ptr getelementptr (i8, ptr @g, i64 4)], align 16
@g = external global [2 x i32]

Expand Down