[llvm] a86ce06 - [SCCP] Use conditional info with AND/OR branch conditions.
Florian Hahn via llvm-commits
llvm-commits at lists.llvm.org
Thu Jul 9 05:07:26 PDT 2020
Author: Florian Hahn
Date: 2020-07-09T12:59:24+01:00
New Revision: a86ce06fafaa051554c6a21d487fa70e998dcafe
URL: https://github.com/llvm/llvm-project/commit/a86ce06fafaa051554c6a21d487fa70e998dcafe
DIFF: https://github.com/llvm/llvm-project/commit/a86ce06fafaa051554c6a21d487fa70e998dcafe.diff
LOG: [SCCP] Use conditional info with AND/OR branch conditions.
Currently SCCP does not combine the information of conditions joined by
AND in the true branch or OR in the false branch.
For branches on AND, 2 copies will be inserted for the true branch, with
one being the operand of the other as in the code below. We can combine
the information using intersection. Note that for the OR case, the
copies are inserted in the false branch, where using intersection is
safe as well.
define void @foo(i32 %a) {
entry:
%lt = icmp ult i32 %a, 100
%gt = icmp ugt i32 %a, 20
%and = and i1 %lt, %gt
; Has predicate info
; branch predicate info { TrueEdge: 1 Comparison: %lt = icmp ult i32 %a, 100 Edge: [label %entry,label %true] }
%a.0 = call i32 @llvm.ssa.copy.140247425954880(i32 %a)
; Has predicate info
; branch predicate info { TrueEdge: 1 Comparison: %gt = icmp ugt i32 %a, 20 Edge: [label %entry,label %false] }
%a.1 = call i32 @llvm.ssa.copy.140247425954880(i32 %a.0)
br i1 %and, label %true, label %false
true: ; preds = %entry
call void @use(i32 %a.1)
%true.1 = icmp ne i32 %a.1, 20
call void @use.i1(i1 %true.1)
ret void
false: ; preds = %entry
call void @use(i32 %a.1)
ret void
}
Reviewers: efriedma, davide, mssimpso, nikic
Reviewed By: nikic
Differential Revision: https://reviews.llvm.org/D77808
Added:
Modified:
llvm/lib/Transforms/Scalar/SCCP.cpp
llvm/test/Transforms/SCCP/conditions-ranges.ll
Removed:
################################################################################
diff --git a/llvm/lib/Transforms/Scalar/SCCP.cpp b/llvm/lib/Transforms/Scalar/SCCP.cpp
index 8ba118291206..5ebd3b71fe78 100644
--- a/llvm/lib/Transforms/Scalar/SCCP.cpp
+++ b/llvm/lib/Transforms/Scalar/SCCP.cpp
@@ -1258,7 +1258,7 @@ void SCCPSolver::handleCallResult(CallBase &CB) {
return;
Value *CopyOf = CB.getOperand(0);
- ValueLatticeElement OriginalVal = getValueState(CopyOf);
+ ValueLatticeElement CopyOfVal = getValueState(CopyOf);
auto *PI = getPredicateInfoFor(&CB);
assert(PI && "Missing predicate info for ssa.copy");
@@ -1271,25 +1271,27 @@ void SCCPSolver::handleCallResult(CallBase &CB) {
Cmp = dyn_cast<CmpInst>(PAssume->Condition);
TrueEdge = true;
} else {
- mergeInValue(ValueState[&CB], &CB, OriginalVal);
+ mergeInValue(ValueState[&CB], &CB, CopyOfVal);
return;
}
// Everything below relies on the condition being a comparison.
if (!Cmp) {
- mergeInValue(ValueState[&CB], &CB, OriginalVal);
+ mergeInValue(ValueState[&CB], &CB, CopyOfVal);
return;
}
+ Value *RenamedOp = PI->RenamedOp;
Value *CmpOp0 = Cmp->getOperand(0);
Value *CmpOp1 = Cmp->getOperand(1);
- if (CopyOf != CmpOp0 && CopyOf != CmpOp1) {
- mergeInValue(ValueState[&CB], &CB, OriginalVal);
+ // Bail out if neither of the operands matches RenamedOp.
+ if (CmpOp0 != RenamedOp && CmpOp1 != RenamedOp) {
+ mergeInValue(ValueState[&CB], &CB, getValueState(CopyOf));
return;
}
auto Pred = Cmp->getPredicate();
- if (CmpOp0 != CopyOf) {
+ if (CmpOp1 == RenamedOp) {
std::swap(CmpOp0, CmpOp1);
Pred = Cmp->getSwappedPredicate();
}
@@ -1300,27 +1302,37 @@ void SCCPSolver::handleCallResult(CallBase &CB) {
return;
}
+ // The code below relies on PredicateInfo only inserting copies for the
+ // true branch when the branch condition is an AND and only inserting
+ // copies for the false branch when the branch condition is an OR. This
+ // ensures we can intersect the range from the condition with the range of
+ // CopyOf.
if (!TrueEdge)
Pred = CmpInst::getInversePredicate(Pred);
ValueLatticeElement CondVal = getValueState(CmpOp1);
ValueLatticeElement &IV = ValueState[&CB];
- if (CondVal.isConstantRange() || OriginalVal.isConstantRange()) {
- auto NewCR =
+ if (CondVal.isConstantRange() || CopyOfVal.isConstantRange()) {
+ auto ImposedCR =
ConstantRange::getFull(DL.getTypeSizeInBits(CopyOf->getType()));
// Get the range imposed by the condition.
if (CondVal.isConstantRange())
- NewCR = ConstantRange::makeAllowedICmpRegion(
+ ImposedCR = ConstantRange::makeAllowedICmpRegion(
Pred, CondVal.getConstantRange());
// Combine range info for the original value with the new range from the
// condition.
- auto OriginalCR = OriginalVal.isConstantRange()
- ? OriginalVal.getConstantRange()
- : ConstantRange::getFull(
- DL.getTypeSizeInBits(CopyOf->getType()));
- NewCR = NewCR.intersectWith(OriginalCR);
+ auto CopyOfCR = CopyOfVal.isConstantRange()
+ ? CopyOfVal.getConstantRange()
+ : ConstantRange::getFull(
+ DL.getTypeSizeInBits(CopyOf->getType()));
+ auto NewCR = ImposedCR.intersectWith(CopyOfCR);
+ // If the existing information is != x, do not use the information from
+ // a chained predicate, as the != x information is more likely to be
+ // helpful in practice.
+ if (!CopyOfCR.contains(NewCR) && CopyOfCR.getSingleMissingElement())
+ NewCR = CopyOfCR;
addAdditionalUser(CmpOp1, &CB);
// TODO: Actually filp MayIncludeUndef for the created range to false,
@@ -1344,7 +1356,7 @@ void SCCPSolver::handleCallResult(CallBase &CB) {
return;
}
- return (void)mergeInValue(IV, &CB, OriginalVal);
+ return (void)mergeInValue(IV, &CB, CopyOfVal);
}
}
diff --git a/llvm/test/Transforms/SCCP/conditions-ranges.ll b/llvm/test/Transforms/SCCP/conditions-ranges.ll
index ea857a100854..612a38f008fc 100644
--- a/llvm/test/Transforms/SCCP/conditions-ranges.ll
+++ b/llvm/test/Transforms/SCCP/conditions-ranges.ll
@@ -814,14 +814,11 @@ define void @f16_conditions_and(i32 %a, i32 %b) {
; CHECK-NEXT: [[BC:%.*]] = and i1 [[LT]], [[GT]]
; CHECK-NEXT: br i1 [[BC]], label [[TRUE:%.*]], label [[FALSE:%.*]]
; CHECK: true:
-; CHECK-NEXT: [[F_1:%.*]] = icmp eq i32 [[A]], 0
-; CHECK-NEXT: call void @use(i1 [[F_1]])
-; CHECK-NEXT: [[F_2:%.*]] = icmp eq i32 [[A]], 20
-; CHECK-NEXT: call void @use(i1 [[F_2]])
+; CHECK-NEXT: call void @use(i1 false)
+; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: call void @use(i1 true)
-; CHECK-NEXT: [[T_2:%.*]] = icmp ne i32 [[A]], 20
-; CHECK-NEXT: call void @use(i1 [[T_2]])
+; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: [[C_1:%.*]] = icmp eq i32 [[A]], 21
; CHECK-NEXT: call void @use(i1 [[C_1]])
; CHECK-NEXT: [[C_2:%.*]] = icmp ugt i32 [[A]], 21
@@ -899,10 +896,8 @@ define void @f17_conditions_or(i32 %a, i32 %b) {
; CHECK: false:
; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: call void @use(i1 false)
-; CHECK-NEXT: [[F_3:%.*]] = icmp ugt i32 [[A]], 100
-; CHECK-NEXT: call void @use(i1 [[F_3]])
-; CHECK-NEXT: [[T_1:%.*]] = icmp ult i32 [[A]], 100
-; CHECK-NEXT: call void @use(i1 [[T_1]])
+; CHECK-NEXT: call void @use(i1 false)
+; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: call void @use(i1 true)
; CHECK-NEXT: [[C_1:%.*]] = icmp eq i32 [[A]], 21
; CHECK-NEXT: call void @use(i1 [[C_1]])
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