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[SimplifyCFG] FoldTwoEntryPHINode(): don't bailout on i1 PHI's if we can hoist a 'not' from incoming values 

Summary:
As it can be seen in the tests in D65143/D65144, even though we have formed an '@llvm.umul.with.overflow'
and got rid of potential for division-by-zero, the control flow remains, we still have that branch.

We have this condition:
```
  // Don't fold i1 branches on PHIs which contain binary operators
  // These can often be turned into switches and other things.
  if (PN->getType()->isIntegerTy(1) &&
      (isa<BinaryOperator>(PN->getIncomingValue(0)) ||
       isa<BinaryOperator>(PN->getIncomingValue(1)) ||
       isa<BinaryOperator>(IfCond)))
    return false;
```
which was added back in rL121764 to help with `select` formation i think?

That check prevents us to flatten the CFG here, even though we know
we no longer need that guard and will be able to drop everything
but the '@llvm.umul.with.overflow' + `not`.

As it can be seen from tests, we end here because the `not` is being
sinked into the PHI's incoming values by InstCombine,
so we can't workaround this by hoisting it to after PHI.

Thus i suggest that we relax that check to not bailout if we'd get to hoist the `not`.

Reviewers: craig.topper, spatel, fhahn, nikic

Reviewed By: spatel

Subscribers: hiraditya, llvm-commits

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D65147

llvm-svn: 370349
This commit is contained in:
Roman Lebedev 2019-08-29 12:47:34 +00:00
parent 473a063a5e
commit 9f35d2b564
3 changed files with 64 additions and 20 deletions
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18
llvm/lib/Transforms/Utils/SimplifyCFG.cpp
View File

@ -2329,12 +2329,24 @@ static bool FoldTwoEntryPHINode(PHINode *PN, const TargetTransformInfo &TTI,
if (!PN)
return true;
// Don't fold i1 branches on PHIs which contain binary operators. These can
// often be turned into switches and other things.
// Return true if at least one of these is a 'not', and another is either
// a 'not' too, or a constant.
auto CanHoistNotFromBothValues = [](Value *V0, Value *V1) {
if (!match(V0, m_Not(m_Value())))
std::swap(V0, V1);
auto Invertible = m_CombineOr(m_Not(m_Value()), m_AnyIntegralConstant());
return match(V0, m_Not(m_Value())) && match(V1, Invertible);
};
// Don't fold i1 branches on PHIs which contain binary operators, unless one
// of the incoming values is an 'not' and another one is freely invertible.
// These can often be turned into switches and other things.
if (PN->getType()->isIntegerTy(1) &&
(isa<BinaryOperator>(PN->getIncomingValue(0)) ||
isa<BinaryOperator>(PN->getIncomingValue(1)) ||
isa<BinaryOperator>(IfCond)))
isa<BinaryOperator>(IfCond)) &&
!CanHoistNotFromBothValues(PN->getIncomingValue(0),
PN->getIncomingValue(1)))
return false;
// If all PHI nodes are promotable, check to make sure that all instructions

60
llvm/test/Transforms/PhaseOrdering/unsigned-multiply-overflow-check.ll
View File

@ -104,18 +104,54 @@ define i1 @will_overflow(i64 %arg, i64 %arg1) {
; SIMPLIFYCFG-NEXT: [[T7:%.*]] = xor i1 [[T6]], true
; SIMPLIFYCFG-NEXT: ret i1 [[T7]]
;
; INSTCOMBINE-LABEL: @will_overflow(
; INSTCOMBINE-NEXT: bb:
; INSTCOMBINE-NEXT: [[T0:%.*]] = icmp eq i64 [[ARG:%.*]], 0
; INSTCOMBINE-NEXT: br i1 [[T0]], label [[BB5:%.*]], label [[BB2:%.*]]
; INSTCOMBINE: bb2:
; INSTCOMBINE-NEXT: [[UMUL:%.*]] = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[ARG]], i64 [[ARG1:%.*]])
; INSTCOMBINE-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; INSTCOMBINE-NEXT: [[PHITMP:%.*]] = xor i1 [[UMUL_OV]], true
; INSTCOMBINE-NEXT: br label [[BB5]]
; INSTCOMBINE: bb5:
; INSTCOMBINE-NEXT: [[T6:%.*]] = phi i1 [ true, [[BB:%.*]] ], [ [[PHITMP]], [[BB2]] ]
; INSTCOMBINE-NEXT: ret i1 [[T6]]
; INSTCOMBINEONLY-LABEL: @will_overflow(
; INSTCOMBINEONLY-NEXT: bb:
; INSTCOMBINEONLY-NEXT: [[T0:%.*]] = icmp eq i64 [[ARG:%.*]], 0
; INSTCOMBINEONLY-NEXT: br i1 [[T0]], label [[BB5:%.*]], label [[BB2:%.*]]
; INSTCOMBINEONLY: bb2:
; INSTCOMBINEONLY-NEXT: [[UMUL:%.*]] = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[ARG]], i64 [[ARG1:%.*]])
; INSTCOMBINEONLY-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; INSTCOMBINEONLY-NEXT: [[PHITMP:%.*]] = xor i1 [[UMUL_OV]], true
; INSTCOMBINEONLY-NEXT: br label [[BB5]]
; INSTCOMBINEONLY: bb5:
; INSTCOMBINEONLY-NEXT: [[T6:%.*]] = phi i1 [ true, [[BB:%.*]] ], [ [[PHITMP]], [[BB2]] ]
; INSTCOMBINEONLY-NEXT: ret i1 [[T6]]
;
; INSTCOMBINESIMPLIFYCFGONLY-LABEL: @will_overflow(
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: bb:
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: [[T0:%.*]] = icmp eq i64 [[ARG:%.*]], 0
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: [[UMUL:%.*]] = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[ARG]], i64 [[ARG1:%.*]])
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: [[PHITMP:%.*]] = xor i1 [[UMUL_OV]], true
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: [[T6:%.*]] = select i1 [[T0]], i1 true, i1 [[PHITMP]]
; INSTCOMBINESIMPLIFYCFGONLY-NEXT: ret i1 [[T6]]
;
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-LABEL: @will_overflow(
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: bb:
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: [[T0:%.*]] = icmp eq i64 [[ARG:%.*]], 0
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: [[UMUL:%.*]] = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[ARG]], i64 [[ARG1:%.*]])
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: [[PHITMP:%.*]] = xor i1 [[UMUL_OV]], true
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: [[T6:%.*]] = or i1 [[T0]], [[PHITMP]]
; INSTCOMBINESIMPLIFYCFGINSTCOMBINE-NEXT: ret i1 [[T6]]
;
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-LABEL: @will_overflow(
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: bb:
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: [[T0:%.*]] = icmp eq i64 [[ARG:%.*]], 0
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: [[UMUL:%.*]] = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[ARG]], i64 [[ARG1:%.*]])
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: [[PHITMP:%.*]] = xor i1 [[UMUL_OV]], true
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: [[T6:%.*]] = select i1 [[T0]], i1 true, i1 [[PHITMP]]
; INSTCOMBINESIMPLIFYCFGCOSTLYONLY-NEXT: ret i1 [[T6]]
;
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-LABEL: @will_overflow(
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: bb:
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: [[T0:%.*]] = icmp eq i64 [[ARG:%.*]], 0
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: [[UMUL:%.*]] = call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[ARG]], i64 [[ARG1:%.*]])
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: [[PHITMP:%.*]] = xor i1 [[UMUL_OV]], true
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: [[T6:%.*]] = or i1 [[T0]], [[PHITMP]]
; INSTCOMBINESIMPLIFYCFGCOSTLYINSTCOMBINE-NEXT: ret i1 [[T6]]
;
bb:
%t0 = icmp eq i64 %arg, 0

6
llvm/test/Transforms/SimplifyCFG/unsigned-multiplication-will-overflow.ll
View File

@ -11,14 +11,10 @@ define i1 @will_overflow(i64 %size, i64 %nmemb) {
; ALL-LABEL: @will_overflow(
; ALL-NEXT: entry:
; ALL-NEXT: [[CMP:%.*]] = icmp eq i64 [[SIZE:%.*]], 0
; ALL-NEXT: br i1 [[CMP]], label [[LAND_END:%.*]], label [[LAND_RHS:%.*]]
; ALL: land.rhs:
; ALL-NEXT: [[UMUL:%.*]] = tail call { i64, i1 } @llvm.umul.with.overflow.i64(i64 [[SIZE]], i64 [[NMEMB:%.*]])
; ALL-NEXT: [[UMUL_OV:%.*]] = extractvalue { i64, i1 } [[UMUL]], 1
; ALL-NEXT: [[UMUL_NOT_OV:%.*]] = xor i1 [[UMUL_OV]], true
; ALL-NEXT: br label [[LAND_END]]
; ALL: land.end:
; ALL-NEXT: [[TMP0:%.*]] = phi i1 [ true, [[ENTRY:%.*]] ], [ [[UMUL_NOT_OV]], [[LAND_RHS]] ]
; ALL-NEXT: [[TMP0:%.*]] = select i1 [[CMP]], i1 true, i1 [[UMUL_NOT_OV]]
; ALL-NEXT: ret i1 [[TMP0]]
;
entry: