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[InstCombine] Fold (select C, (gep Ptr, Idx), Ptr) -> (gep Ptr, (select C, Idx, 0)) (PR50183) (REAPPLIED) 

As discussed on PR50183, we already fold to prefer 'select-of-idx' vs 'select-of-gep':

define <4 x i32>* @select0a(<4 x i32>* %a0, i64 %a1, i1 %a2, i64 %a3) {
  %gep0 = getelementptr inbounds <4 x i32>, <4 x i32>* %a0, i64 %a1
  %gep1 = getelementptr inbounds <4 x i32>, <4 x i32>* %a0, i64 %a3
  %sel = select i1 %a2, <4 x i32>* %gep0, <4 x i32>* %gep1
  ret <4 x i32>* %sel
}
-->
define <4 x i32>* @select1a(<4 x i32>* %a0, i64 %a1, i1 %a2, i64 %a3) {
  %sel = select i1 %a2, i64 %a1, i64 %a3
  %gep = getelementptr inbounds <4 x i32>, <4 x i32>* %a0, i64 %sel
  ret <4 x i32>* %gep
}

This patch adds basic handling for the 'fallthrough' cases where the gep idx == 0 has been folded away to the base address:

define <4 x i32>* @select0(<4 x i32>* %a0, i64 %a1, i1 %a2) {
  %gep = getelementptr inbounds <4 x i32>, <4 x i32>* %a0, i64 %a1
  %sel = select i1 %a2, <4 x i32>* %a0, <4 x i32>* %gep
  ret <4 x i32>* %sel
}
-->
define <4 x i32>* @select1(<4 x i32>* %a0, i64 %a1, i1 %a2) {
  %sel = select i1 %a2, i64 0, i64 %a1
  %gep = getelementptr inbounds <4 x i32>, <4 x i32>* %a0, i64 %sel
  ret <4 x i32>* %gep
}

Reapplied with a fix for the bpf "-bpf-disable-avoid-speculation" tests

Differential Revision: https://reviews.llvm.org/D105901
This commit is contained in:
Simon Pilgrim 2021-07-14 12:20:47 +01:00
parent 12d04ce956
commit d561b6fbdb
4 changed files with 43 additions and 14 deletions
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27
llvm/lib/Transforms/InstCombine/InstCombineSelect.cpp
View File

@ -2933,6 +2933,33 @@ Instruction *InstCombinerImpl::visitSelectInst(SelectInst &SI) {
if (Instruction *I = foldSelectExtConst(SI))
return I;
// Fold (select C, (gep Ptr, Idx), Ptr) -> (gep Ptr, (select C, Idx, 0))
// Fold (select C, Ptr, (gep Ptr, Idx)) -> (gep Ptr, (select C, 0, Idx))
auto SelectGepWithBase = [&](GetElementPtrInst *Gep, Value *Base,
bool Swap) -> GetElementPtrInst * {
Value *Ptr = Gep->getPointerOperand();
if (Gep->getNumOperands() != 2 || Gep->getPointerOperand() != Base ||
!Gep->hasOneUse())
return nullptr;
Type *ElementType = Gep->getResultElementType();
Value *Idx = Gep->getOperand(1);
Value *NewT = Idx;
Value *NewF = Constant::getNullValue(Idx->getType());
if (Swap)
std::swap(NewT, NewF);
Value *NewSI =
Builder.CreateSelect(CondVal, NewT, NewF, SI.getName() + ".idx", &SI);
return Gep->isInBounds()
? GetElementPtrInst::CreateInBounds(ElementType, Ptr, {NewSI})
: GetElementPtrInst::Create(ElementType, Ptr, {NewSI});
};
if (auto *TrueGep = dyn_cast<GetElementPtrInst>(TrueVal))
if (auto *NewGep = SelectGepWithBase(TrueGep, FalseVal, false))
return NewGep;
if (auto *FalseGep = dyn_cast<GetElementPtrInst>(FalseVal))
if (auto *NewGep = SelectGepWithBase(FalseGep, TrueVal, true))
return NewGep;
// See if we can fold the select into one of our operands.
if (SelType->isIntOrIntVectorTy() || SelType->isFPOrFPVectorTy()) {
if (Instruction *FoldI = foldSelectIntoOp(SI, TrueVal, FalseVal))

10
llvm/test/CodeGen/BPF/adjust-opt-speculative1.ll
View File

@ -49,12 +49,12 @@ if.end: ; preds = %if.then, %entry
; CHECK: [[LABEL]]:
; CHECK: r0 = [[REG6]]
; CHECK-DISABLE: r0 = [[REG6]]
; CHECK-DISABLE: r0 += [[REG1:r[0-9]+]]
; CHECK-DISABLE: [[REG2:r[0-9]+]] = 8
; CHECK-DISABLE: if [[REG2]] > [[REG1]] goto [[LABEL:.*]]
; CHECK-DISABLE: r0 = [[REG6]]
; CHECK-DISABLE: [[REG1:r[0-9]+]] = 8
; CHECK-DISABLE: if [[REG1]] > r0 goto [[LABEL:.*]]
; CHECK-DISABLE: r0 = 0
; CHECK-DISABLE: [[LABEL]]:
; CHECK-DISABLE: [[REG6]] += r0
; CHECK-DISABLE: r0 = [[REG6]]
; CHECK-COMMON: exit

8
llvm/test/CodeGen/BPF/adjust-opt-speculative2.ll
View File

@ -56,12 +56,14 @@ if.end: ; preds = %if.then, %entry
; CHECK-DISABLE: [[REG1:r[0-9]+]] = r0
; CHECK-DISABLE: [[REG1]] <<= 32
; CHECK-DISABLE: [[REG1]] >>= 32
; CHECK-DISABLE: r0 = [[REG6]]
; CHECK-DISABLE: r0 += [[REG1]]
; CHECK-DISABLE: [[REG2:r[0-9]+]] = 8
; CHECK-DISABLE: if [[REG2]] > [[REG1]] goto [[LABEL:.*]]
; CHECK-DISABLE: r0 = [[REG6]]
; CHECK-DISABLE: r0 = 0
; CHECK-DISABLE: [[LABEL]]:
; CHECK-DISABLE: r0 <<= 32
; CHECK-DISABLE: r0 >>= 32
; CHECK-DISABLE: [[REG6]] += r0
; CHECK-DISABLE: r0 = [[REG6]]
; CHECK-COMMON: exit

12
llvm/test/Transforms/InstCombine/select-gep.ll
View File

@ -74,9 +74,9 @@ define i32* @test2(i32* %p, i64 %x, i64 %y) {
; PR50183
define i32* @test2a(i32* %p, i64 %x, i64 %y) {
; CHECK-LABEL: @test2a(
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i32, i32* [[P:%.*]], i64 [[X:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[X]], [[Y:%.*]]
; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[CMP]], i32* [[GEP]], i32* [[P]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[SELECT_IDX:%.*]] = select i1 [[CMP]], i64 [[X]], i64 0
; CHECK-NEXT: [[SELECT:%.*]] = getelementptr inbounds i32, i32* [[P:%.*]], i64 [[SELECT_IDX]]
; CHECK-NEXT: ret i32* [[SELECT]]
;
%gep = getelementptr inbounds i32, i32* %p, i64 %x
@ -88,9 +88,9 @@ define i32* @test2a(i32* %p, i64 %x, i64 %y) {
; PR50183
define i32* @test2b(i32* %p, i64 %x, i64 %y) {
; CHECK-LABEL: @test2b(
; CHECK-NEXT: [[GEP:%.*]] = getelementptr inbounds i32, i32* [[P:%.*]], i64 [[X:%.*]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[X]], [[Y:%.*]]
; CHECK-NEXT: [[SELECT:%.*]] = select i1 [[CMP]], i32* [[P]], i32* [[GEP]]
; CHECK-NEXT: [[CMP:%.*]] = icmp ugt i64 [[X:%.*]], [[Y:%.*]]
; CHECK-NEXT: [[SELECT_IDX:%.*]] = select i1 [[CMP]], i64 0, i64 [[X]]
; CHECK-NEXT: [[SELECT:%.*]] = getelementptr inbounds i32, i32* [[P:%.*]], i64 [[SELECT_IDX]]
; CHECK-NEXT: ret i32* [[SELECT]]
;
%gep = getelementptr inbounds i32, i32* %p, i64 %x