[llvm] r359969 - [CodeGenPrepare] limit overflow intrinsic matching to a single basic block (2nd try)
Sanjay Patel via llvm-commits
llvm-commits at lists.llvm.org
Sat May 4 05:46:32 PDT 2019
Author: spatel
Date: Sat May 4 05:46:32 2019
New Revision: 359969
URL: http://llvm.org/viewvc/llvm-project?rev=359969&view=rev
Log:
[CodeGenPrepare] limit overflow intrinsic matching to a single basic block (2nd try)
This is a subset of the original commit from rL359879
which was reverted because it could crash when using the 'RemovedInstructions'
structure that enables delayed deletion of dead instructions. The motivating
compile-time win does not require that change though. We should get most of
that win from this change alone.
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.
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=359969&r1=359968&r2=359969&view=diff
==============================================================================
--- llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp (original)
+++ llvm/trunk/lib/CodeGen/CodeGenPrepare.cpp Sat May 4 05:46:32 2019
@@ -1177,6 +1177,20 @@ 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);
@@ -1186,36 +1200,15 @@ 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);
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=359969&r1=359968&r2=359969&view=diff
==============================================================================
--- llvm/trunk/test/CodeGen/X86/cgp-usubo.ll (original)
+++ llvm/trunk/test/CodeGen/X86/cgp-usubo.ll Sat May 4 05:46:32 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=359969&r1=359968&r2=359969&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll (original)
+++ llvm/trunk/test/Transforms/CodeGenPrepare/X86/optimizeSelect-DT.ll Sat May 4 05:46:32 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=359969&r1=359968&r2=359969&view=diff
==============================================================================
--- llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll (original)
+++ llvm/trunk/test/Transforms/CodeGenPrepare/X86/overflow-intrinsics.ll Sat May 4 05:46:32 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
@@ -514,6 +514,26 @@ exit:
ret void
}
+; This was crashing when trying to delay instruction removal/deletion.
+
+declare i64 @llvm.objectsize.i64.p0i8(i8*, i1 immarg, i1 immarg, i1 immarg) #0
+
+define hidden fastcc void @crash() {
+; CHECK-LABEL: @crash(
+; CHECK-NEXT: [[TMP1:%.*]] = call { i64, i1 } @llvm.uadd.with.overflow.i64(i64 undef, i64 undef)
+; CHECK-NEXT: [[MATH:%.*]] = extractvalue { i64, i1 } [[TMP1]], 0
+; CHECK-NEXT: [[OV:%.*]] = extractvalue { i64, i1 } [[TMP1]], 1
+; CHECK-NEXT: [[T2:%.*]] = select i1 undef, i1 undef, i1 [[OV]]
+; CHECK-NEXT: unreachable
+;
+ %t0 = add i64 undef, undef
+ %t1 = icmp ult i64 %t0, undef
+ %t2 = select i1 undef, i1 undef, i1 %t1
+ %t3 = call i64 @llvm.objectsize.i64.p0i8(i8* nonnull undef, i1 false, i1 false, i1 false)
+ %t4 = icmp ugt i64 %t3, 7
+ unreachable
+}
+
; Check that every instruction inserted by -codegenprepare has a debug location.
; DEBUG: CheckModuleDebugify: PASS
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