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[X86] Don't attempt to fold sub(C1, xor(X, C2)) with opaque constants

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Fixes PR49451
This commit is contained in:
Simon Pilgrim 2021-03-11 11:56:58 +00:00
parent 3b0fb3a8e1
commit 32e46239ea
2 changed files with 120 additions and 4 deletions
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16
lib/Target/X86/X86ISelLowering.cpp
View File

@ -49097,14 +49097,22 @@ static SDValue combineSub(SDNode *N, SelectionDAG &DAG,
SDValue Op0 = N->getOperand(0);
SDValue Op1 = N->getOperand(1);
// TODO: Add NoOpaque handling to isConstantIntBuildVectorOrConstantInt.
auto IsNonOpaqueConstant = [&](SDValue Op) {
if (SDNode *C = DAG.isConstantIntBuildVectorOrConstantInt(Op)) {
if (auto *Cst = dyn_cast<ConstantSDNode>(C))
return !Cst->isOpaque();
return true;
}
return false;
};
// X86 can't encode an immediate LHS of a sub. See if we can push the
// negation into a preceding instruction. If the RHS of the sub is a XOR with
// one use and a constant, invert the immediate, saving one register.
// sub(C1, xor(X, C2)) -> add(xor(X, ~C2), C1+1)
if (Op1.getOpcode() == ISD::XOR &&
DAG.isConstantIntBuildVectorOrConstantInt(Op0) &&
DAG.isConstantIntBuildVectorOrConstantInt(Op1.getOperand(1)) &&
Op1->hasOneUse()) {
if (Op1.getOpcode() == ISD::XOR && IsNonOpaqueConstant(Op0) &&
IsNonOpaqueConstant(Op1.getOperand(1)) && Op1->hasOneUse()) {
SDLoc DL(N);
EVT VT = Op0.getValueType();
SDValue NewXor = DAG.getNode(ISD::XOR, SDLoc(Op1), VT, Op1.getOperand(0),

108
test/CodeGen/X86/pr49451.ll Normal file
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@ -0,0 +1,108 @@
; NOTE: Assertions have been autogenerated by utils/update_llc_test_checks.py
; RUN: llc < %s -mtriple=i686-unknown-unknown | FileCheck %s --check-prefix=X86
; RUN: llc < %s -mtriple=x86_64-unknown-unknown | FileCheck %s --check-prefix=X64
@s_0 = external dso_local local_unnamed_addr global i16, align 2
@s_2 = external dso_local local_unnamed_addr global i16, align 2
define void @func_6(i8 %uc_8, i64 %uli_10) nounwind {
; X86-LABEL: func_6:
; X86: # %bb.0: # %entry
; X86-NEXT: pushl %ebx
; X86-NEXT: pushl %esi
; X86-NEXT: movl {{[0-9]+}}(%esp), %eax
; X86-NEXT: movl $-1, %ecx
; X86-NEXT: xorl %edx, %edx
; X86-NEXT: xorl %ebx, %ebx
; X86-NEXT: # implicit-def: $si
; X86-NEXT: .p2align 4, 0x90
; X86-NEXT: .LBB0_1: # %for.body612
; X86-NEXT: # =>This Inner Loop Header: Depth=1
; X86-NEXT: testb %dl, %dl
; X86-NEXT: je .LBB0_2
; X86-NEXT: # %bb.3: # %if.end1401
; X86-NEXT: # in Loop: Header=BB0_1 Depth=1
; X86-NEXT: testb %dl, %dl
; X86-NEXT: addl %eax, %esi
; X86-NEXT: movw %si, s_2
; X86-NEXT: movw %bx, s_0
; X86-NEXT: incl %ecx
; X86-NEXT: incl %ebx
; X86-NEXT: cmpw $73, %cx
; X86-NEXT: jl .LBB0_1
; X86-NEXT: # %bb.4: # %for.body1703
; X86-NEXT: .LBB0_2: # %if.then671
;
; X64-LABEL: func_6:
; X64: # %bb.0: # %entry
; X64-NEXT: movl $23090, %eax # imm = 0x5A32
; X64-NEXT: xorl %ecx, %ecx
; X64-NEXT: # implicit-def: $dx
; X64-NEXT: .p2align 4, 0x90
; X64-NEXT: .LBB0_1: # %for.body612
; X64-NEXT: # =>This Inner Loop Header: Depth=1
; X64-NEXT: testb %cl, %cl
; X64-NEXT: je .LBB0_2
; X64-NEXT: # %bb.3: # %if.end1401
; X64-NEXT: # in Loop: Header=BB0_1 Depth=1
; X64-NEXT: testb %cl, %cl
; X64-NEXT: addl %esi, %edx
; X64-NEXT: movw %dx, {{.*}}(%rip)
; X64-NEXT: leal -23090(%rax), %edi
; X64-NEXT: movw %di, {{.*}}(%rip)
; X64-NEXT: incq %rax
; X64-NEXT: leal -23091(%rax), %edi
; X64-NEXT: cmpw $73, %di
; X64-NEXT: jl .LBB0_1
; X64-NEXT: # %bb.4: # %for.body1703
; X64-NEXT: .LBB0_2: # %if.then671
entry:
%conv649 = zext i8 %uc_8 to i64
%xor650 = xor i64 %conv649, 296357731680175678
%i = trunc i64 %uli_10 to i16
br label %for.body612
for.body612: ; preds = %for.inc1677, %entry
%i1 = phi i16 [ undef, %entry ], [ %conv1532, %for.inc1677 ]
%i2 = phi i16 [ -1, %entry ], [ %add1679, %for.inc1677 ]
br label %if.then635
if.then635: ; preds = %for.body612
%conv653 = sext i16 %i2 to i64
%cmp654.not = icmp eq i64 %xor650, %conv653
%conv653.op = xor i64 %conv653, 296357731680175678
%tobool670.not = icmp eq i64 undef, 0
br i1 %tobool670.not, label %if.end1401, label %if.then671
if.then671: ; preds = %if.then635
%cmp830 = icmp sgt i16 %i1, 21
unreachable
if.end1401: ; preds = %if.then635
%conv1421 = sext i16 %i2 to i32
%or1422 = or i32 %conv1421, undef
br label %if.end1510
if.end1510: ; preds = %if.end1401
br i1 undef, label %cond.false1514, label %cond.end1528
cond.false1514: ; preds = %if.end1510
%conv1525 = sext i16 %i2 to i64
%add1526 = add nsw i64 %conv1525, 23091
br label %cond.end1528
cond.end1528: ; preds = %cond.false1514, %if.end1510
%cond1529 = phi i64 [ %add1526, %cond.false1514 ], [ undef, %if.end1510 ]
%conv1532 = add i16 %i1, %i
store i16 %conv1532, i16* @s_2, align 2
br label %for.inc1677
for.inc1677: ; preds = %cond.end1528
%add1679 = add i16 %i2, 1
store i16 %add1679, i16* @s_0, align 2
%cmp610 = icmp slt i16 %add1679, 73
br i1 %cmp610, label %for.body612, label %for.body1703
for.body1703: ; preds = %for.inc1677
unreachable
}