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[SCCP] Use constant ranges for PHI nodes.
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For PHIs with multiple incoming values, we can improve precision by
using constant ranges for integers. We can over-approximate phis
by merging the incoming values.

Reviewers: davide, efriedma, mssimpso

Reviewed By: efriedma

Differential Revision: https://reviews.llvm.org/D71933
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@fhahn
fhahn committed Mar 19, 2020
1 parent b1c8a37 commit 4a58996
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Showing 6 changed files with 312 additions and 43 deletions.
38 changes: 9 additions & 29 deletions llvm/lib/Transforms/Scalar/SCCP.cpp
View file
Expand Up @@ -739,9 +739,8 @@ void SCCPSolver::visitPHINode(PHINode &PN) {
if (PN.getType()->isStructTy())
return (void)markOverdefined(&PN);

if (isOverdefined(getValueState(&PN))) {
return (void)markOverdefined(&PN);
}
if (getValueState(&PN).isOverdefined())
return; // Quick exit

// Super-extra-high-degree PHI nodes are unlikely to ever be marked constant,
// and slow us down a lot. Just mark them overdefined.
Expand All @@ -753,38 +752,19 @@ void SCCPSolver::visitPHINode(PHINode &PN) {
// constant, and they agree with each other, the PHI becomes the identical
// constant. If they are constant and don't agree, the PHI is overdefined.
// If there are no executable operands, the PHI remains unknown.
Constant *OperandVal = nullptr;
bool Changed = false;
for (unsigned i = 0, e = PN.getNumIncomingValues(); i != e; ++i) {
LatticeVal IV = getValueState(PN.getIncomingValue(i));
if (IV.isUnknownOrUndef()) continue; // Doesn't influence PHI node.

if (!isEdgeFeasible(PN.getIncomingBlock(i), PN.getParent()))
continue;

if (isOverdefined(IV)) // PHI node becomes overdefined!
return (void)markOverdefined(&PN);

if (!OperandVal) { // Grab the first value.
OperandVal = getConstant(IV);
continue;
}

// There is already a reachable operand. If we conflict with it,
// then the PHI node becomes overdefined. If we agree with it, we
// can continue on.

// Check to see if there are two different constants merging, if so, the PHI
// node is overdefined.
if (getConstant(IV) != OperandVal)
return (void)markOverdefined(&PN);
LatticeVal &Res = getValueState(&PN);
Changed |= Res.mergeIn(IV, DL);
if (Res.isOverdefined())
break;
}

// If we exited the loop, this means that the PHI node only has constant
// arguments that agree with each other(and OperandVal is the constant) or
// OperandVal is null because there are no defined incoming arguments. If
// this is the case, the PHI remains unknown.
if (OperandVal)
markConstant(&PN, OperandVal); // Acquire operand value
if (Changed)
pushToWorkListMsg(ValueState[&PN], &PN);
}

void SCCPSolver::visitReturnInst(ReturnInst &I) {
Expand Down
9 changes: 3 additions & 6 deletions llvm/test/Transforms/SCCP/binaryops-range-special-cases.ll
View file
Expand Up @@ -44,8 +44,7 @@ define void @sdiv1_cmp_range_1(i32 %x, i1 %c) {
; CHECK: bb3:
; CHECK-NEXT: [[P:%.*]] = phi i32 [ 1, [[BB1]] ], [ 2, [[BB2]] ]
; CHECK-NEXT: [[D:%.*]] = sdiv i32 1, [[X:%.*]]
; CHECK-NEXT: [[C_0:%.*]] = icmp slt i32 [[P]], [[D]]
; CHECK-NEXT: call void @use(i1 [[C_0]])
; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: [[C_1:%.*]] = icmp eq i32 [[P]], [[D]]
; CHECK-NEXT: call void @use(i1 [[C_1]])
; CHECK-NEXT: ret void
Expand Down Expand Up @@ -77,10 +76,8 @@ define void @sdiv1_cmp_range_2(i32 %x, i1 %c) {
; CHECK: bb3:
; CHECK-NEXT: [[P:%.*]] = phi i32 [ 3, [[BB1]] ], [ 2, [[BB2]] ]
; CHECK-NEXT: [[D:%.*]] = sdiv i32 1, [[X:%.*]]
; CHECK-NEXT: [[C_0:%.*]] = icmp slt i32 [[P]], [[D]]
; CHECK-NEXT: call void @use(i1 [[C_0]])
; CHECK-NEXT: [[C_1:%.*]] = icmp eq i32 [[P]], [[D]]
; CHECK-NEXT: call void @use(i1 [[C_1]])
; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: call void @use(i1 false)
; CHECK-NEXT: ret void
;
br i1 %c, label %bb1, label %bb2
Expand Down
9 changes: 3 additions & 6 deletions llvm/test/Transforms/SCCP/ip-constant-ranges.ll
View file
Expand Up @@ -59,12 +59,9 @@ entry:
ret i32 %res.2
}

; x is overdefined, because constant ranges are only used for parameter
; values.
; CHECK-LABEL: f3
; CHECK: %cmp = icmp sgt i32 %x, 300
; CHECK: %res = select i1 %cmp, i32 1, i32 2
; CHECK: ret i32 %res
; CHECK-LABEL: entry:
; CHECK: ret i32 undef
define internal i32 @f3(i32 %x) {
entry:
%cmp = icmp sgt i32 %x, 300
Expand All @@ -83,7 +80,7 @@ if.true:
end:
%res = phi i32 [ 0, %entry], [ 1, %if.true ]
%call1 = tail call i32 @f3(i32 %res)
ret i32 %call1
ret i32 2
}

; CHECK-LABEL: f4
Expand Down
215 changes: 215 additions & 0 deletions llvm/test/Transforms/SCCP/ip-ranges-phis.ll
View file
@@ -0,0 +1,215 @@
; RUN: opt < %s -ipsccp -S | FileCheck %s

define internal i32 @f1(i32 %x) {
; CHECK-LABEL: define internal i32 @f1(
; CHECK-NEXT: ret i32 undef
;
%cmp = icmp sgt i32 %x, 300
%res = select i1 %cmp, i32 1, i32 2
ret i32 %res
}

; %res is a constant range [0, 2) from a PHI node.
define i32 @caller1(i1 %cmp) {
; CHECK-LABEL: define i32 @caller1(
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 %cmp, label %if.true, label %end

; CHECK-LABEL: if.true:
; CHECK-NEXT: br label %end

; CHECK-LABEL: end:
; CHECK-NEXT: %res = phi i32 [ 0, %entry ], [ 1, %if.true ]
; CHECK-NEXT: %call1 = tail call i32 @f1(i32 %res)
; CHECK-NEXT: ret i32 2
;
entry:
br i1 %cmp, label %if.true, label %end

if.true:
br label %end

end:
%res = phi i32 [ 0, %entry], [ 1, %if.true ]
%call1 = tail call i32 @f1(i32 %res)
ret i32 %call1
}

define internal i32 @f2(i32 %x, i32 %y, i32 %z, i1 %cmp.1, i1 %cmp.2) {
; CHECK-LABEL: define internal i32 @f2(
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 %cmp.1, label %if.true.1, label %end

; CHECK-LABEL: if.true.1:
; CHECK-NEXT: br i1 %cmp.2, label %if.true.2, label %end

; CHECK-LABEL: if.true.2:
; CHECK-NEXT: br label %end

; CHECK-LABEL: end:
; CHECK-NEXT: %p = phi i32 [ %x, %entry ], [ %y, %if.true.1 ], [ %z, %if.true.2 ]
; CHECK-NEXT: %c.1 = icmp sgt i32 %p, 5
; CHECK-NEXT: %c.2 = icmp eq i32 %p, 0
; CHECK-NEXT: %c.3 = icmp slt i32 %p, 0
; CHECK-NEXT: %v.1 = select i1 %c.1, i32 10, i32 100
; CHECK-NEXT: %v.2 = select i1 %c.2, i32 20, i32 200
; CHECK-NEXT: %v.3 = select i1 %c.3, i32 30, i32 300
; CHECK-NEXT: %r.1 = add i32 %v.1, %v.2
; CHECK-NEXT: %r.2 = add i32 %r.1, %v.3
; CHECK-NEXT: %r.3 = add i32 %r.2, 400
; CHECK-NEXT: %r.4 = add i32 %r.3, 50
; CHECK-NEXT: %r.5 = add i32 %r.4, 60
; CHECK-NEXT: %r.6 = add i32 %r.4, 700
; CHECK-NEXT: ret i32 %r.6
;
entry:
br i1 %cmp.1, label %if.true.1, label %end

if.true.1:
br i1 %cmp.2, label %if.true.2, label %end

if.true.2:
br label %end

end:
%p = phi i32 [ %x, %entry ], [ %y, %if.true.1 ], [ %z, %if.true.2 ]
%c.1 = icmp sgt i32 %p, 5
%c.2 = icmp eq i32 %p, 0
%c.3 = icmp slt i32 %p, 0
%c.4 = icmp sgt i32 %p, 10
%c.5 = icmp sle i32 %p, 10
%c.6 = icmp sgt i32 %p, -11
%c.7 = icmp slt i32 %p, -11
%v.1 = select i1 %c.1, i32 10, i32 100
%v.2 = select i1 %c.2, i32 20, i32 200
%v.3 = select i1 %c.3, i32 30, i32 300
%v.4 = select i1 %c.4, i32 40, i32 400
%v.5 = select i1 %c.5, i32 50, i32 500
%v.6 = select i1 %c.6, i32 60, i32 600
%v.7 = select i1 %c.7, i32 70, i32 700
%r.1 = add i32 %v.1, %v.2
%r.2 = add i32 %r.1, %v.3
%r.3 = add i32 %r.2, %v.4
%r.4 = add i32 %r.3, %v.5
%r.5 = add i32 %r.4, %v.6
%r.6 = add i32 %r.4, %v.7
ret i32 %r.6
}

define i32 @caller2(i1 %cmp.1, i1 %cmp.2) {
; CHECK-LABEL: define i32 @caller2(i1 %cmp.1, i1 %cmp.2) {
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 %cmp.1, label %if.true, label %end

; CHECK-LABEL: if.true: ; preds = %entry
; CHECK-NEXT: br label %end

; CHECK-LABEL: end: ; preds = %if.true, %entry
; CHECK-NEXT: %p1 = phi i32 [ 0, %entry ], [ 1, %if.true ]
; CHECK-NEXT: %p2 = phi i32 [ 1, %entry ], [ -10, %if.true ]
; CHECK-NEXT: %p3 = phi i32 [ 1, %entry ], [ 10, %if.true ]
; CHECK-NEXT: %call1 = tail call i32 @f2(i32 %p1, i32 %p2, i32 %p3, i1 %cmp.1, i1 %cmp.2)
; CHECK-NEXT: ret i32 %call1
;

entry:
br i1 %cmp.1, label %if.true, label %end

if.true:
br label %end

end:
%p1 = phi i32 [ 0, %entry], [ 1, %if.true ]
%p2 = phi i32 [ 1, %entry], [ -10, %if.true ]
%p3 = phi i32 [ 1, %entry], [ 10, %if.true ]
%call1 = tail call i32 @f2(i32 %p1, i32 %p2, i32 %p3, i1 %cmp.1, i1 %cmp.2)
ret i32 %call1
}

define internal i32 @f3(i32 %x, i32 %y, i1 %cmp.1) {
; CHECK-LABEL: define internal i32 @f3(i32 %x, i32 %y, i1 %cmp.1) {
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 %cmp.1, label %if.true.1, label %end

; CHECK-LABEL: if.true.1: ; preds = %entry
; CHECK-NEXT: br label %end

; CHECK-LABEL: end: ; preds = %if.true.1, %entry
; CHECK-NEXT: %p = phi i32 [ %x, %entry ], [ %y, %if.true.1 ]
; CHECK-NEXT: %c.1 = icmp sgt i32 %p, 5
; CHECK-NEXT: %c.2 = icmp eq i32 %p, 0
; CHECK-NEXT: %c.3 = icmp slt i32 %p, 0
; CHECK-NEXT: %c.4 = icmp sgt i32 %p, 10
; CHECK-NEXT: %c.5 = icmp sle i32 %p, 10
; CHECK-NEXT: %c.6 = icmp sgt i32 %p, -11
; CHECK-NEXT: %c.7 = icmp slt i32 %p, -11
; CHECK-NEXT: %v.1 = select i1 %c.1, i32 10, i32 100
; CHECK-NEXT: %v.2 = select i1 %c.2, i32 20, i32 200
; CHECK-NEXT: %v.3 = select i1 %c.3, i32 30, i32 300
; CHECK-NEXT: %v.4 = select i1 %c.4, i32 40, i32 400
; CHECK-NEXT: %v.5 = select i1 %c.5, i32 50, i32 500
; CHECK-NEXT: %v.6 = select i1 %c.6, i32 60, i32 600
; CHECK-NEXT: %v.7 = select i1 %c.7, i32 70, i32 700
; CHECK-NEXT: %r.1 = add i32 %v.1, %v.2
; CHECK-NEXT: %r.2 = add i32 %r.1, %v.3
; CHECK-NEXT: %r.3 = add i32 %r.2, %v.4
; CHECK-NEXT: %r.4 = add i32 %r.3, %v.5
; CHECK-NEXT: %r.5 = add i32 %r.4, %v.6
; CHECK-NEXT: %r.6 = add i32 %r.4, %v.7
; CHECK-NEXT: ret i32 %r.6
;
entry:
br i1 %cmp.1, label %if.true.1, label %end

if.true.1:
br label %end

end:
%p = phi i32 [ %x, %entry ], [ %y, %if.true.1 ]
%c.1 = icmp sgt i32 %p, 5
%c.2 = icmp eq i32 %p, 0
%c.3 = icmp slt i32 %p, 0
%c.4 = icmp sgt i32 %p, 10
%c.5 = icmp sle i32 %p, 10
%c.6 = icmp sgt i32 %p, -11
%c.7 = icmp slt i32 %p, -11
%v.1 = select i1 %c.1, i32 10, i32 100
%v.2 = select i1 %c.2, i32 20, i32 200
%v.3 = select i1 %c.3, i32 30, i32 300
%v.4 = select i1 %c.4, i32 40, i32 400
%v.5 = select i1 %c.5, i32 50, i32 500
%v.6 = select i1 %c.6, i32 60, i32 600
%v.7 = select i1 %c.7, i32 70, i32 700
%r.1 = add i32 %v.1, %v.2
%r.2 = add i32 %r.1, %v.3
%r.3 = add i32 %r.2, %v.4
%r.4 = add i32 %r.3, %v.5
%r.5 = add i32 %r.4, %v.6
%r.6 = add i32 %r.4, %v.7
ret i32 %r.6
}

define i32 @caller3(i32 %y, i1 %cmp.1) {
; CHECK-LABEL: define i32 @caller3(i32 %y, i1 %cmp.1) {
; CHECK-LABEL: entry:
; CHECK-NEXT: br i1 %cmp.1, label %if.true, label %end

; CHECK-LABEL: if.true:
; CHECK-NEXT: br label %end

; CHECK-LABEL: end:
; CHECK-NEXT: %p1 = phi i32 [ 0, %entry ], [ 5, %if.true ]
; CHECK-NEXT: %call1 = tail call i32 @f3(i32 %p1, i32 %y, i1 %cmp.1)
; CHECK-NEXT: ret i32 %call1
;
entry:
br i1 %cmp.1, label %if.true, label %end

if.true:
br label %end

end:
%p1 = phi i32 [ 0, %entry], [ 5, %if.true ]
%call1 = tail call i32 @f3(i32 %p1, i32 %y, i1 %cmp.1)
ret i32 %call1
}

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