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[DivRemPairs] Don't assert that we won't ever get expanded-form rem pairs in different BB's (PR43500)

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If we happen to have the same div in two basic blocks,
and in one of those we also happen to have the rem part,
we'd match the div-rem pair, but the wrong ones.
So let's drop overly-ambiguous assert.

Fixes https://bugs.llvm.org/show_bug.cgi?id=43500

llvm-svn: 373167
This commit is contained in:
Roman Lebedev 2019-09-29 15:25:24 +00:00
parent 4cfaf409b9
commit 408398f5f4
2 changed files with 36 additions and 2 deletions
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2
lib/Transforms/Scalar/DivRemPairs.cpp
View File

@ -233,8 +233,6 @@ static bool optimizeDivRem(Function &F, const TargetTransformInfo &TTI,
if (!DivDominates && !DT.dominates(RemInst, DivInst)) { if (!DivDominates && !DT.dominates(RemInst, DivInst)) {
// We have matching div-rem pair, but they are in two different blocks, // We have matching div-rem pair, but they are in two different blocks,
// neither of which dominates one another. // neither of which dominates one another.
assert(!RemOriginallyWasInExpandedForm &&
"Won't happen for expanded-form rem.");
// FIXME: We could hoist both ops to the common predecessor block? // FIXME: We could hoist both ops to the common predecessor block?
continue; continue;
} }

36
test/Transforms/DivRemPairs/X86/div-expanded-rem-pair.ll
View File

@ -168,3 +168,39 @@ end:
%ret = phi i128 [ %rem, %if ], [ 3, %entry ] %ret = phi i128 [ %rem, %if ], [ 3, %entry ]
ret i128 %ret ret i128 %ret
} }
; Even in expanded form, we can end up with div and rem in different basic
; blocks neither of which dominates each another.
define i32 @can_have_divrem_in_mutually_nondominating_bbs(i1 %cmp, i32 %a, i32 %b) {
; CHECK-LABEL: @can_have_divrem_in_mutually_nondominating_bbs(
; CHECK-NEXT: entry:
; CHECK-NEXT: br i1 [[CMP:%.*]], label [[IF_THEN:%.*]], label [[IF_ELSE:%.*]]
; CHECK: if.then:
; CHECK-NEXT: [[T0:%.*]] = udiv i32 [[A:%.*]], [[B:%.*]]
; CHECK-NEXT: [[T1:%.*]] = mul nuw i32 [[T0]], [[B]]
; CHECK-NEXT: [[T2_RECOMPOSED:%.*]] = urem i32 [[A]], [[B]]
; CHECK-NEXT: br label [[END:%.*]]
; CHECK: if.else:
; CHECK-NEXT: [[T3:%.*]] = udiv i32 [[A]], [[B]]
; CHECK-NEXT: br label [[END]]
; CHECK: end:
; CHECK-NEXT: [[RET:%.*]] = phi i32 [ [[T2_RECOMPOSED]], [[IF_THEN]] ], [ [[T3]], [[IF_ELSE]] ]
; CHECK-NEXT: ret i32 [[RET]]
;
entry:
br i1 %cmp, label %if.then, label %if.else
if.then:
%t0 = udiv i32 %a, %b
%t1 = mul nuw i32 %t0, %b
%t2 = sub i32 %a, %t1
br label %end
if.else:
%t3 = udiv i32 %a, %b
br label %end
end:
%ret = phi i32 [ %t2, %if.then ], [ %t3, %if.else ]
ret i32 %ret
}