[llvm] r359879 - [CodeGenPrepare] limit overflow intrinsic matching to a single basic block
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Fri May 3 06:09:19 PDT 2019
Author: spatel
Date: Fri May 3 06:09:18 2019
New Revision: 359879
URL: http://llvm.org/viewvc/llvm-project?rev=359879&view=rev
Log:
[CodeGenPrepare] limit overflow intrinsic matching to a single basic block
Using/updating a dominator tree to match math overflow patterns may be very
expensive in compile-time (because of the way CGP uses a DT), so just handle
the single-block case.
Also, we were restarting the iterator loops when doing the overflow intrinsic
transforms by marking the dominator tree for update. That was done to prevent
iterating over a removed instruction. But we can postpone the deletion using
the existing "RemovedInsts" structure, and that means we don't need to update
the DT.
See post-commit thread for rL354298 for more details:
http://lists.llvm.org/pipermail/llvm-commits/Week-of-Mon-20190422/646276.html
Differential Revision: https://reviews.llvm.org/D61075
Modified:
llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
llvm/trunk/test/CodeGen/X86/cgp-usubo.ll
llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll
llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll
Modified: llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp?rev=359879&r1=359878&r2=359879&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp (original)
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp Fri May 3 06:09:18 2019
@@ -388,9 +388,9 @@ class TypePromotionTransaction;
bool tryToSinkFreeOperands(Instruction *I);
bool replaceMathCmpWithIntrinsic(BinaryOperator *BO, CmpInst *Cmp,
Intrinsic::ID IID);
- bool optimizeCmp(CmpInst *Cmp, bool &ModifiedDT);
- bool combineToUSubWithOverflow(CmpInst *Cmp, bool &ModifiedDT);
- bool combineToUAddWithOverflow(CmpInst *Cmp, bool &ModifiedDT);
+ bool optimizeCmp(CmpInst *Cmp);
+ bool combineToUSubWithOverflow(CmpInst *Cmp);
+ bool combineToUAddWithOverflow(CmpInst *Cmp);
};
} // end anonymous namespace
@@ -484,9 +484,13 @@ bool CodeGenPrepare::runOnFunction(Funct
if (!LargeOffsetGEPMap.empty())
MadeChange |= splitLargeGEPOffsets();
- // Really free removed instructions during promotion.
- for (Instruction *I : RemovedInsts)
+ // Really free instructions removed during promotion or kept around to
+ // improve efficiency (see comments in overflow intrinsic transforms).
+ for (Instruction *I : RemovedInsts) {
+ if (I->getParent())
+ I->removeFromParent();
I->deleteValue();
+ }
EverMadeChange |= MadeChange;
SeenChainsForSExt.clear();
@@ -1177,6 +1181,20 @@ static bool OptimizeNoopCopyExpression(C
bool CodeGenPrepare::replaceMathCmpWithIntrinsic(BinaryOperator *BO,
CmpInst *Cmp,
Intrinsic::ID IID) {
+ if (BO->getParent() != Cmp->getParent()) {
+ // We used to use a dominator tree here to allow multi-block optimization.
+ // But that was problematic because:
+ // 1. It could cause a perf regression by hoisting the math op into the
+ // critical path.
+ // 2. It could cause a perf regression by creating a value that was live
+ // across multiple blocks and increasing register pressure.
+ // 3. Use of a dominator tree could cause large compile-time regression.
+ // This is because we recompute the DT on every change in the main CGP
+ // run-loop. The recomputing is probably unnecessary in many cases, so if
+ // that was fixed, using a DT here would be ok.
+ return false;
+ }
+
// We allow matching the canonical IR (add X, C) back to (usubo X, -C).
Value *Arg0 = BO->getOperand(0);
Value *Arg1 = BO->getOperand(1);
@@ -1186,45 +1204,28 @@ bool CodeGenPrepare::replaceMathCmpWithI
Arg1 = ConstantExpr::getNeg(cast<Constant>(Arg1));
}
- Instruction *InsertPt;
- if (BO->hasOneUse() && BO->user_back() == Cmp) {
- // If the math is only used by the compare, insert at the compare to keep
- // the condition in the same block as its users. (CGP aggressively sinks
- // compares to help out SDAG.)
- InsertPt = Cmp;
- } else {
- // The math and compare may be independent instructions. Check dominance to
- // determine the insertion point for the intrinsic.
- bool MathDominates = getDT(*BO->getFunction()).dominates(BO, Cmp);
- if (!MathDominates && !getDT(*BO->getFunction()).dominates(Cmp, BO))
- return false;
-
- BasicBlock *MathBB = BO->getParent(), *CmpBB = Cmp->getParent();
- if (MathBB != CmpBB) {
- // Avoid hoisting an extra op into a dominating block and creating a
- // potentially longer critical path.
- if (!MathDominates)
- return false;
- // Check that the insertion doesn't create a value that is live across
- // more than two blocks, so to minimise the increase in register pressure.
- BasicBlock *Dominator = MathDominates ? MathBB : CmpBB;
- BasicBlock *Dominated = MathDominates ? CmpBB : MathBB;
- auto Successors = successors(Dominator);
- if (llvm::find(Successors, Dominated) == Successors.end())
- return false;
+ // Insert at the first instruction of the pair.
+ Instruction *InsertPt = nullptr;
+ for (Instruction &Iter : *Cmp->getParent()) {
+ if (&Iter == BO || &Iter == Cmp) {
+ InsertPt = &Iter;
+ break;
}
-
- InsertPt = MathDominates ? cast<Instruction>(BO) : cast<Instruction>(Cmp);
}
+ assert(InsertPt != nullptr && "Parent block did not contain cmp or binop");
IRBuilder<> Builder(InsertPt);
Value *MathOV = Builder.CreateBinaryIntrinsic(IID, Arg0, Arg1);
Value *Math = Builder.CreateExtractValue(MathOV, 0, "math");
Value *OV = Builder.CreateExtractValue(MathOV, 1, "ov");
+
+ // Delay the actual removal/deletion of the binop and compare for efficiency.
+ // If we delete those now, we would invalidate the instruction iterator and
+ // trigger dominator tree updates.
BO->replaceAllUsesWith(Math);
Cmp->replaceAllUsesWith(OV);
- BO->eraseFromParent();
- Cmp->eraseFromParent();
+ RemovedInsts.insert(BO);
+ RemovedInsts.insert(Cmp);
return true;
}
@@ -1260,8 +1261,7 @@ static bool matchUAddWithOverflowConstan
/// Try to combine the compare into a call to the llvm.uadd.with.overflow
/// intrinsic. Return true if any changes were made.
-bool CodeGenPrepare::combineToUAddWithOverflow(CmpInst *Cmp,
- bool &ModifiedDT) {
+bool CodeGenPrepare::combineToUAddWithOverflow(CmpInst *Cmp) {
Value *A, *B;
BinaryOperator *Add;
if (!match(Cmp, m_UAddWithOverflow(m_Value(A), m_Value(B), m_BinOp(Add))))
@@ -1281,13 +1281,10 @@ bool CodeGenPrepare::combineToUAddWithOv
if (!replaceMathCmpWithIntrinsic(Add, Cmp, Intrinsic::uadd_with_overflow))
return false;
- // Reset callers - do not crash by iterating over a dead instruction.
- ModifiedDT = true;
return true;
}
-bool CodeGenPrepare::combineToUSubWithOverflow(CmpInst *Cmp,
- bool &ModifiedDT) {
+bool CodeGenPrepare::combineToUSubWithOverflow(CmpInst *Cmp) {
// We are not expecting non-canonical/degenerate code. Just bail out.
Value *A = Cmp->getOperand(0), *B = Cmp->getOperand(1);
if (isa<Constant>(A) && isa<Constant>(B))
@@ -1342,8 +1339,6 @@ bool CodeGenPrepare::combineToUSubWithOv
if (!replaceMathCmpWithIntrinsic(Sub, Cmp, Intrinsic::usub_with_overflow))
return false;
- // Reset callers - do not crash by iterating over a dead instruction.
- ModifiedDT = true;
return true;
}
@@ -1413,14 +1408,14 @@ static bool sinkCmpExpression(CmpInst *C
return MadeChange;
}
-bool CodeGenPrepare::optimizeCmp(CmpInst *Cmp, bool &ModifiedDT) {
+bool CodeGenPrepare::optimizeCmp(CmpInst *Cmp) {
if (sinkCmpExpression(Cmp, *TLI))
return true;
- if (combineToUAddWithOverflow(Cmp, ModifiedDT))
+ if (combineToUAddWithOverflow(Cmp))
return true;
- if (combineToUSubWithOverflow(Cmp, ModifiedDT))
+ if (combineToUSubWithOverflow(Cmp))
return true;
return false;
@@ -6945,7 +6940,7 @@ bool CodeGenPrepare::optimizeInst(Instru
}
if (auto *Cmp = dyn_cast<CmpInst>(I))
- if (TLI && optimizeCmp(Cmp, ModifiedDT))
+ if (TLI && optimizeCmp(Cmp))
return true;
if (LoadInst *LI = dyn_cast<LoadInst>(I)) {
Modified: llvm/trunk/test/CodeGen/X86/cgp-usubo.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/CodeGen/X86/cgp-usubo.ll?rev=359879&r1=359878&r2=359879&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/cgp-usubo.ll (original)
+++ llvm/trunk/test/CodeGen/X86/cgp-usubo.ll Fri May 3 06:09:18 2019
@@ -121,7 +121,7 @@ define i1 @usubo_ne_constant0_op1_i32(i3
ret i1 %ov
}
-; Verify insertion point for multi-BB.
+; This used to verify insertion point for multi-BB, but now we just bail out.
declare void @call(i1)
@@ -131,14 +131,17 @@ define i1 @usubo_ult_sub_dominates_i64(i
; CHECK-NEXT: testb $1, %cl
; CHECK-NEXT: je .LBB8_2
; CHECK-NEXT: # %bb.1: # %t
-; CHECK-NEXT: subq %rsi, %rdi
-; CHECK-NEXT: setb %al
-; CHECK-NEXT: movq %rdi, (%rdx)
+; CHECK-NEXT: movq %rdi, %rax
+; CHECK-NEXT: subq %rsi, %rax
+; CHECK-NEXT: movq %rax, (%rdx)
; CHECK-NEXT: testb $1, %cl
-; CHECK-NEXT: jne .LBB8_3
+; CHECK-NEXT: je .LBB8_2
+; CHECK-NEXT: # %bb.3: # %end
+; CHECK-NEXT: cmpq %rsi, %rdi
+; CHECK-NEXT: setb %al
+; CHECK-NEXT: retq
; CHECK-NEXT: .LBB8_2: # %f
; CHECK-NEXT: movl %ecx, %eax
-; CHECK-NEXT: .LBB8_3: # %end
; CHECK-NEXT: retq
entry:
br i1 %cond, label %t, label %f
Modified: llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll?rev=359879&r1=359878&r2=359879&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll (original)
+++ llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll Fri May 3 06:09:18 2019
@@ -14,11 +14,10 @@ define i1 @PR41004(i32 %x, i32 %y, i32 %
; CHECK-NEXT: br label [[SELECT_END]]
; CHECK: select.end:
; CHECK-NEXT: [[MUL:%.*]] = phi i32 [ [[REM]], [[SELECT_TRUE_SINK]] ], [ 0, [[ENTRY:%.*]] ]
-; CHECK-NEXT: [[TMP0:%.*]] = call { i32, i1 } @llvm.usub.with.overflow.i32(i32 [[T1:%.*]], i32 1)
-; CHECK-NEXT: [[MATH:%.*]] = extractvalue { i32, i1 } [[TMP0]], 0
-; CHECK-NEXT: [[OV:%.*]] = extractvalue { i32, i1 } [[TMP0]], 1
-; CHECK-NEXT: [[ADD:%.*]] = add i32 [[MATH]], [[MUL]]
-; CHECK-NEXT: ret i1 [[OV]]
+; CHECK-NEXT: [[NEG:%.*]] = add i32 [[T1:%.*]], -1
+; CHECK-NEXT: [[ADD:%.*]] = add i32 [[NEG]], [[MUL]]
+; CHECK-NEXT: [[TOBOOL:%.*]] = icmp eq i32 [[T1]], 0
+; CHECK-NEXT: ret i1 [[TOBOOL]]
;
entry:
%rem = srem i32 %x, 2
Modified: llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll?rev=359879&r1=359878&r2=359879&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll (original)
+++ llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll Fri May 3 06:09:18 2019
@@ -47,15 +47,16 @@ define i64 @uaddo3(i64 %a, i64 %b) nounw
ret i64 %Q
}
+; TODO? CGP sinks the compare before we have a chance to form the overflow intrinsic.
+
define i64 @uaddo4(i64 %a, i64 %b, i1 %c) nounwind ssp {
; CHECK-LABEL: @uaddo4(
; CHECK-NEXT: entry:
+; CHECK-NEXT: [[ADD:%.*]] = add i64 [[B:%.*]], [[A:%.*]]
; CHECK-NEXT: br i1 [[C:%.*]], label [[NEXT:%.*]], label [[EXIT:%.*]]
; CHECK: next:
-; CHECK-NEXT: [[TMP0:%.*]] = call { i64, i1 } @llvm.uadd.with.overflow.i64(i64 [[B:%.*]], i64 [[A:%.*]])
-; CHECK-NEXT: [[MATH:%.*]] = extractvalue { i64, i1 } [[TMP0]], 0
-; CHECK-NEXT: [[OV:%.*]] = extractvalue { i64, i1 } [[TMP0]], 1
-; CHECK-NEXT: [[Q:%.*]] = select i1 [[OV]], i64 [[B]], i64 42
+; CHECK-NEXT: [[TMP0:%.*]] = icmp ugt i64 [[B]], [[ADD]]
+; CHECK-NEXT: [[Q:%.*]] = select i1 [[TMP0]], i64 [[B]], i64 42
; CHECK-NEXT: ret i64 [[Q]]
; CHECK: exit:
; CHECK-NEXT: ret i64 0
@@ -362,7 +363,7 @@ define i1 @usubo_ne_constant0_op1_i32(i3
ret i1 %ov
}
-; Verify insertion point for multi-BB.
+; This used to verify insertion point for multi-BB, but now we just bail out.
declare void @call(i1)
@@ -371,15 +372,14 @@ define i1 @usubo_ult_sub_dominates_i64(i
; CHECK-NEXT: entry:
; CHECK-NEXT: br i1 [[COND:%.*]], label [[T:%.*]], label [[F:%.*]]
; CHECK: t:
-; CHECK-NEXT: [[TMP0:%.*]] = call { i64, i1 } @llvm.usub.with.overflow.i64(i64 [[X:%.*]], i64 [[Y:%.*]])
-; CHECK-NEXT: [[MATH:%.*]] = extractvalue { i64, i1 } [[TMP0]], 0
-; CHECK-NEXT: [[OV1:%.*]] = extractvalue { i64, i1 } [[TMP0]], 1
-; CHECK-NEXT: store i64 [[MATH]], i64* [[P:%.*]]
+; CHECK-NEXT: [[S:%.*]] = sub i64 [[X:%.*]], [[Y:%.*]]
+; CHECK-NEXT: store i64 [[S]], i64* [[P:%.*]]
; CHECK-NEXT: br i1 [[COND]], label [[END:%.*]], label [[F]]
; CHECK: f:
; CHECK-NEXT: ret i1 [[COND]]
; CHECK: end:
-; CHECK-NEXT: ret i1 [[OV1]]
+; CHECK-NEXT: [[OV:%.*]] = icmp ult i64 [[X]], [[Y]]
+; CHECK-NEXT: ret i1 [[OV]]
;
entry:
br i1 %cond, label %t, label %f
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