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[x86] Fix EFLAGS copy lowering to correctly handle walking past uses in

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multiple successors where some of the uses end up killing the EFLAGS
register.

There was a bug where rather than skipping to the next basic block
queued up with uses once we saw a kill, we stopped processing the blocks
entirely. =/

Test case produces completely nonsensical code w/o this tiny fix.

This was found testing Speculative Load Hardening and split out of that
work.

Differential Revision: https://reviews.llvm.org/D49211

llvm-svn: 336874
This commit is contained in:
Chandler Carruth 2018-07-12 00:52:50 +00:00
parent 723bd78241
commit 40027cf33a
2 changed files with 80 additions and 1 deletions
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2
lib/Target/X86/X86FlagsCopyLowering.cpp
View File

@ -555,7 +555,7 @@ bool X86FlagsCopyLoweringPass::runOnMachineFunction(MachineFunction &MF) {
// If the flags were killed, we're done with this block.
if (FlagsKilled)
break;
continue;
// Otherwise we need to scan successors for ones where the flags live-in
// and queue those up for processing.

79
test/CodeGen/X86/flags-copy-lowering.mir
View File

@ -72,6 +72,12 @@
call void @foo()
ret void
}
define i64 @test_branch_with_livein_and_kill(i64 %a, i64 %b) {
entry:
call void @foo()
ret i64 0
}
...
---
name: test_branch
@ -553,3 +559,76 @@ body: |
RET 0
...
---
name: test_branch_with_livein_and_kill
# CHECK-LABEL: name: test_branch_with_livein_and_kill
liveins:
- { reg: '$rdi', virtual-reg: '%0' }
- { reg: '$rsi', virtual-reg: '%1' }
body: |
bb.0:
successors: %bb.1, %bb.2, %bb.3
liveins: $rdi, $rsi
%0:gr64 = COPY $rdi
%1:gr64 = COPY $rsi
CMP64rr %0, %1, implicit-def $eflags
%2:gr64 = COPY $eflags
; CHECK-NOT: COPY{{( killed)?}} $eflags
; CHECK: %[[S_REG:[^:]*]]:gr8 = SETSr implicit $eflags
; CHECK-NEXT: %[[NE_REG:[^:]*]]:gr8 = SETNEr implicit $eflags
; CHECK-NEXT: %[[A_REG:[^:]*]]:gr8 = SETAr implicit $eflags
; CHECK-NEXT: %[[B_REG:[^:]*]]:gr8 = SETBr implicit $eflags
; CHECK-NOT: COPY{{( killed)?}} $eflags
ADJCALLSTACKDOWN64 0, 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
CALL64pcrel32 @foo, csr_64, implicit $rsp, implicit $ssp, implicit $rdi, implicit-def $rsp, implicit-def $ssp, implicit-def $eax
ADJCALLSTACKUP64 0, 0, implicit-def dead $rsp, implicit-def dead $eflags, implicit-def dead $ssp, implicit $rsp, implicit $ssp
$eflags = COPY %2
JA_1 %bb.1, implicit $eflags
JB_1 %bb.2, implicit $eflags
JMP_1 %bb.3
; CHECK-NOT: $eflags =
;
; CHECK: TEST8rr %[[A_REG]], %[[A_REG]], implicit-def $eflags
; CHECK-NEXT: JNE_1 %bb.1, implicit killed $eflags
; CHECK-SAME: {{$[[:space:]]}}
; CHECK-NEXT: bb.4:
; CHECK-NEXT: successors: {{.*$}}
; CHECK-SAME: {{$[[:space:]]}}
; CHECK-NEXT: TEST8rr %[[B_REG]], %[[B_REG]], implicit-def $eflags
; CHECK-NEXT: JNE_1 %bb.2, implicit killed $eflags
; CHECK-NEXT: JMP_1 %bb.3
bb.1:
liveins: $eflags
%3:gr64 = CMOVE64rr %0, %1, implicit killed $eflags
; CHECK-NOT: $eflags =
; CHECK: TEST8rr %[[NE_REG]], %[[NE_REG]], implicit-def $eflags
; CHECK-NEXT: %3:gr64 = CMOVE64rr %0, %1, implicit killed $eflags
$rax = COPY %3
RET 0, $rax
bb.2:
liveins: $eflags
%4:gr64 = CMOVNE64rr %0, %1, implicit killed $eflags
; CHECK-NOT: $eflags =
; CHECK: TEST8rr %[[NE_REG]], %[[NE_REG]], implicit-def $eflags
; CHECK-NEXT: %4:gr64 = CMOVNE64rr %0, %1, implicit killed $eflags
$rax = COPY %4
RET 0, $rax
bb.3:
liveins: $eflags
%5:gr64 = CMOVS64rr %0, %1, implicit killed $eflags
; CHECK-NOT: $eflags =
; CHECK: TEST8rr %[[S_REG]], %[[S_REG]], implicit-def $eflags
; CHECK-NEXT: %5:gr64 = CMOVNE64rr %0, %1, implicit killed $eflags
$rax = COPY %5
RET 0, $rax
...