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[BPF] simplify zero extension with MOV_32_64

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The current pattern matching for zext results in the following code snippet
being produced,

  w1 = w0
  r1 <<= 32
  r1 >>= 32

Because BPF implementations require zero extension on 32bit loads this
both adds a few extra unneeded instructions but also makes it a bit
harder for the verifier to track the r1 register bounds. For example in
this verifier trace we see at the end of the snippet R2 offset is unknown.
However, if we track this correctly we see w1 should have the same bounds
as r8. R8 smax is less than U32 max value so a zero extend load should keep
the same value. Adding a max value of 800 (R8=inv(id=0,smax_value=800)) to
an off=0, as seen in R7 should create a max offset of 800. However at the
end of the snippet we note the R2 max offset is 0xffffFFFF.

  R0=inv(id=0,smax_value=800)
  R1_w=inv(id=0,umax_value=2147483647,var_off=(0x0; 0x7fffffff))
  R6=ctx(id=0,off=0,imm=0) R7=map_value(id=0,off=0,ks=4,vs=1600,imm=0)
  R8_w=inv(id=0,smax_value=800,umax_value=4294967295,var_off=(0x0; 0xffffffff))
  R9=inv800 R10=fp0 fp-8=mmmm????
 58: (1c) w9 -= w8
 59: (bc) w1 = w8
 60: (67) r1 <<= 32
 61: (77) r1 >>= 32
 62: (bf) r2 = r7
 63: (0f) r2 += r1
 64: (bf) r1 = r6
 65: (bc) w3 = w9
 66: (b7) r4 = 0
 67: (85) call bpf_get_stack#67
  R0=inv(id=0,smax_value=800)
  R1_w=ctx(id=0,off=0,imm=0)
  R2_w=map_value(id=0,off=0,ks=4,vs=1600,umax_value=4294967295,var_off=(0x0; 0xffffffff))
  R3_w=inv(id=0,umax_value=800,var_off=(0x0; 0x3ff))
  R4_w=inv0 R6=ctx(id=0,off=0,imm=0)
  R7=map_value(id=0,off=0,ks=4,vs=1600,imm=0)
  R8_w=inv(id=0,smax_value=800,umax_value=4294967295,var_off=(0x0; 0xffffffff))
  R9_w=inv(id=0,umax_value=800,var_off=(0x0; 0x3ff))
  R10=fp0 fp-8=mmmm????

After this patch R1 bounds are not smashed by the <<=32 >>=32 shift and we
get correct bounds on R2 umax_value=800.

Further it reduces 3 insns to 1.

Signed-off-by: John Fastabend <john.fastabend@gmail.com>

Differential Revision: https://reviews.llvm.org/D73985
This commit is contained in:
John Fastabend 2020-05-27 11:18:16 -07:00 committed by Yonghong Song
parent 57b2436f12
commit d6d187a5b7
9 changed files with 66 additions and 34 deletions
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6
lib/Target/BPF/BPFISelLowering.cpp
View File

@ -604,6 +604,12 @@ BPFTargetLowering::EmitSubregExt(MachineInstr &MI, MachineBasicBlock *BB,
DebugLoc DL = MI.getDebugLoc();
MachineRegisterInfo &RegInfo = F->getRegInfo();
if (!isSigned) {
Register PromotedReg0 = RegInfo.createVirtualRegister(RC);
BuildMI(BB, DL, TII.get(BPF::MOV_32_64), PromotedReg0).addReg(Reg);
return PromotedReg0;
}
Register PromotedReg0 = RegInfo.createVirtualRegister(RC);
Register PromotedReg1 = RegInfo.createVirtualRegister(RC);
Register PromotedReg2 = RegInfo.createVirtualRegister(RC);

3
lib/Target/BPF/BPFInstrInfo.td
View File

@ -732,8 +732,7 @@ let isCodeGenOnly = 1 in {
def : Pat<(i64 (sext GPR32:$src)),
(SRA_ri (SLL_ri (MOV_32_64 GPR32:$src), 32), 32)>;
def : Pat<(i64 (zext GPR32:$src)),
(SRL_ri (SLL_ri (MOV_32_64 GPR32:$src), 32), 32)>;
def : Pat<(i64 (zext GPR32:$src)), (MOV_32_64 GPR32:$src)>;
// For i64 -> i32 truncation, use the 32-bit subregister directly.
def : Pat<(i32 (trunc GPR:$src)),

15
lib/Target/BPF/BPFMIPeephole.cpp
View File

@ -301,19 +301,16 @@ bool BPFMIPreEmitPeephole::eliminateRedundantMov(void) {
//
// MOV rA, rA
//
// This is particularly possible to happen when sub-register support
// enabled. The special type cast insn MOV_32_64 involves different
// register class on src (i32) and dst (i64), RA could generate useless
// instruction due to this.
// Note that we cannot remove
// MOV_32_64 rA, wA
// MOV_rr_32 wA, wA
// as these two instructions having side effects, zeroing out
// top 32 bits of rA.
unsigned Opcode = MI.getOpcode();
if (Opcode == BPF::MOV_32_64 ||
Opcode == BPF::MOV_rr || Opcode == BPF::MOV_rr_32) {
if (Opcode == BPF::MOV_rr) {
Register dst = MI.getOperand(0).getReg();
Register src = MI.getOperand(1).getReg();
if (Opcode == BPF::MOV_32_64)
dst = TRI->getSubReg(dst, BPF::sub_32);
if (dst != src)
continue;

20
test/CodeGen/BPF/32-bit-subreg-cond-select.ll
View File

@ -56,8 +56,9 @@ entry:
ret i32 %c.d
}
; CHECK-LABEL: select_cc_32
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
; Function Attrs: norecurse nounwind readnone
define dso_local i64 @select_cc_32_64(i32 %a, i32 %b, i64 %c, i64 %d) local_unnamed_addr #0 {
@ -67,8 +68,9 @@ entry:
ret i64 %c.d
}
; CHECK-LABEL: select_cc_32_64
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
; Function Attrs: norecurse nounwind readnone
define dso_local i32 @select_cc_64_32(i64 %a, i64 %b, i32 %c, i32 %d) local_unnamed_addr #0 {
@ -88,8 +90,9 @@ entry:
ret i32 %c.d
}
; CHECK-LABEL: selecti_cc_32
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
; Function Attrs: norecurse nounwind readnone
define dso_local i64 @selecti_cc_32_64(i32 %a, i64 %c, i64 %d) local_unnamed_addr #0 {
@ -99,8 +102,9 @@ entry:
ret i64 %c.d
}
; CHECK-LABEL: selecti_cc_32_64
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
; Function Attrs: norecurse nounwind readnone
define dso_local i32 @selecti_cc_64_32(i64 %a, i32 %c, i32 %d) local_unnamed_addr #0 {

2
test/CodeGen/BPF/32-bit-subreg-peephole-phi-1.ll
View File

@ -27,7 +27,7 @@ entry:
%call = tail call i32 @helper(i32 %conv)
ret i32 %call
}
; CHECK: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} >>= 32
; CHECK: if r{{[0-9]+}} == r{{[0-9]+}} goto

4
test/CodeGen/BPF/32-bit-subreg-peephole-phi-2.ll
View File

@ -27,8 +27,8 @@ entry:
%call = tail call i32 @helper(i32 %conv)
ret i32 %call
}
; CHECK: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK: if r{{[0-9]+}} == r{{[0-9]+}} goto
declare dso_local i32 @helper(i32) local_unnamed_addr

5
test/CodeGen/BPF/32-bit-subreg-peephole-phi-3.ll
View File

@ -44,8 +44,9 @@ for.body: ; preds = %for.body, %entry
%exitcond = icmp eq i64 %inc, 100
br i1 %exitcond, label %for.cond.cleanup, label %for.body, !llvm.loop !2
}
; CHECK: [[VAL:r[0-9]+]] <<= 32
; CHECK: [[VAL]] >>= 32
; CHECK: [[VAL:r[0-9]+]] = w{{[0-9]+}}
; CHECK-NOT: [[VAL:r[0-9]+]] <<= 32
; CHECK-NOT: [[VAL]] >>= 32
; CHECK: if [[VAL]] == 0 goto
!2 = distinct !{!2, !3}

24
test/CodeGen/BPF/32-bit-subreg-peephole.ll
View File

@ -47,8 +47,9 @@ define dso_local i64 @select_u(i32 %a, i32 %b, i64 %c, i64 %d) local_unnamed_add
entry:
%cmp = icmp ugt i32 %a, %b
%c.d = select i1 %cmp, i64 %c, i64 %d
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
; CHECK: if r{{[0-9]+}} {{<|>}} r{{[0-9]+}} goto
ret i64 %c.d
}
@ -58,8 +59,9 @@ define dso_local i64 @select_u_2(i32 %a, i64 %b, i64 %c, i64 %d) local_unnamed_a
; CHECK-LABEL: select_u_2:
entry:
%conv = zext i32 %a to i64
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
%cmp = icmp ugt i64 %conv, %b
%c.d = select i1 %cmp, i64 %c, i64 %d
ret i64 %c.d
@ -84,10 +86,11 @@ entry:
%call = tail call i64 bitcast (i64 (...)* @bar to i64 ()*)() #2
%conv = trunc i64 %call to i32
%cmp = icmp ult i32 %conv, 10
; The shifts can't be optimized out because %call comes from function call
; returning i64 so the high bits might be valid.
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; %call comes from function call returning i64 so the high bits will need
; to be cleared.
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
%b.c = select i1 %cmp, i32 %b, i32 %c
; CHECK: if r{{[0-9]+}} {{<|>}} {{[0-9]+}} goto
ret i32 %b.c
@ -100,8 +103,9 @@ define dso_local i32* @inc_p(i32* readnone %p, i32 %a) local_unnamed_addr #0 {
; CHECK-LABEL: inc_p:
entry:
%idx.ext = zext i32 %a to i64
; CHECK: r{{[0-9]+}} <<= 32
; CHECK-NEXT: r{{[0-9]+}} >>= 32
; CHECK: r{{[0-9]+}} = w{{[0-9]+}}
; CHECK-NOT: r{{[0-9]+}} <<= 32
; CHECK-NOT: r{{[0-9]+}} >>= 32
%add.ptr = getelementptr inbounds i32, i32* %p, i64 %idx.ext
ret i32* %add.ptr
}

21
test/CodeGen/BPF/32-bit-subreg-zext.ll Normal file
View File

@ -0,0 +1,21 @@
; RUN: llc -O2 -march=bpfel -mattr=+alu32 < %s | FileCheck %s
; RUN: llc -O2 -march=bpfel -mcpu=v3 < %s | FileCheck %s
; RUN: llc -O2 -march=bpfeb -mattr=+alu32 < %s | FileCheck %s
; RUN: llc -O2 -march=bpfeb -mcpu=v3 < %s | FileCheck %s
;
; long zext(unsigned int a)
; {
; long b = a;
; return b;
; }
; Function Attrs: norecurse nounwind
define dso_local i64 @zext(i32 %a) local_unnamed_addr #0 {
entry:
%conv = zext i32 %a to i64
; CHECK-NOT: r[[#]] <<= 32
; CHECK-NOT: r[[#]] >>= 32
ret i64 %conv
}
attributes #0 = { norecurse nounwind }