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[LoopDeletion] Support selects when symbolically evaluating 1st iteration 

Adds support for selects for which we know value on the 1st iteration.

Differential Revision: https://reviews.llvm.org/D104111
Reviewed By: nikic
This commit is contained in:
Max Kazantsev 2021-10-09 14:47:44 +07:00
parent 49ca01047f
commit 4c0da23663
2 changed files with 12 additions and 5 deletions
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8
llvm/lib/Transforms/Scalar/LoopDeletion.cpp
View File

@ -197,6 +197,14 @@ getValueOnFirstIteration(Value *V, DenseMap<Value *, Value *> &FirstIterValue,
Value *RHS =
getValueOnFirstIteration(Cmp->getOperand(1), FirstIterValue, SQ);
FirstIterV = SimplifyICmpInst(Cmp->getPredicate(), LHS, RHS, SQ);
} else if (auto *Select = dyn_cast<SelectInst>(V)) {
Value *Cond =
getValueOnFirstIteration(Select->getCondition(), FirstIterValue, SQ);
if (auto *C = dyn_cast<ConstantInt>(Cond)) {
auto *Selected = C->isAllOnesValue() ? Select->getTrueValue()
: Select->getFalseValue();
FirstIterV = getValueOnFirstIteration(Selected, FirstIterValue, SQ);
}
}
if (!FirstIterV)
FirstIterV = V;

9
llvm/test/Transforms/LoopDeletion/eval_first_iteration.ll
View File

@ -979,25 +979,24 @@ failure:
unreachable
}
; TODO: We can break the backedge here.
define i32 @test_select_const(i32 %x) {
; CHECK-LABEL: @test_select_const(
; CHECK-NEXT: entry:
; CHECK-NEXT: br label [[LOOP:%.*]]
; CHECK: loop:
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ], [ [[SUM_NEXT:%.*]], [[BACKEDGE:%.*]] ]
; CHECK-NEXT: [[SUM:%.*]] = phi i32 [ 0, [[ENTRY:%.*]] ]
; CHECK-NEXT: [[SUB:%.*]] = sub i32 4, [[SUM]]
; CHECK-NEXT: [[IS_POSITIVE:%.*]] = icmp sgt i32 [[SUB]], 0
; CHECK-NEXT: [[SEL:%.*]] = select i1 [[IS_POSITIVE]], i32 [[SUB]], i32 [[X:%.*]]
; CHECK-NEXT: [[SEL_COND:%.*]] = icmp sgt i32 [[SEL]], 0
; CHECK-NEXT: br i1 [[SEL_COND]], label [[BACKEDGE]], label [[IF_FALSE:%.*]]
; CHECK-NEXT: br i1 [[SEL_COND]], label [[BACKEDGE:%.*]], label [[IF_FALSE:%.*]]
; CHECK: if.false:
; CHECK-NEXT: br label [[BACKEDGE]]
; CHECK: backedge:
; CHECK-NEXT: [[MERGE_PHI:%.*]] = phi i32 [ 0, [[IF_FALSE]] ], [ [[SUB]], [[LOOP]] ]
; CHECK-NEXT: [[SUM_NEXT]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[SUM_NEXT:%.*]] = add i32 [[SUM]], [[MERGE_PHI]]
; CHECK-NEXT: [[LOOP_COND:%.*]] = icmp ne i32 [[SUM_NEXT]], 4
; CHECK-NEXT: br i1 [[LOOP_COND]], label [[LOOP]], label [[DONE:%.*]]
; CHECK-NEXT: br label [[DONE:%.*]]
; CHECK: done:
; CHECK-NEXT: [[SUM_NEXT_LCSSA:%.*]] = phi i32 [ [[SUM_NEXT]], [[BACKEDGE]] ]
; CHECK-NEXT: ret i32 [[SUM_NEXT_LCSSA]]