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Add command line option --no-trap-after-noreturn #67051

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merged 2 commits into from
Sep 22, 2023
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Add command line option --no-trap-after-noreturn #67051

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cd9c53d
Add command line option --no-trap-after-noreturn
majaha Sep 21, 2023
7a46fcc
Test --no-trap-after-noreturn for misfires
majaha Sep 21, 2023
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7 changes: 7 additions & 0 deletions llvm/lib/CodeGen/LLVMTargetMachine.cpp
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Original file line number Diff line number Diff line change
Expand Up @@ -37,6 +37,11 @@ static cl::opt<bool>
EnableTrapUnreachable("trap-unreachable", cl::Hidden,
cl::desc("Enable generating trap for unreachable"));

static cl::opt<bool> EnableNoTrapAfterNoreturn(
"no-trap-after-noreturn", cl::Hidden,
cl::desc("Do not emit a trap instruction for 'unreachable' IR instructions "
"after noreturn calls, even if --trap-unreachable is set."));

void LLVMTargetMachine::initAsmInfo() {
MRI.reset(TheTarget.createMCRegInfo(getTargetTriple().str()));
assert(MRI && "Unable to create reg info");
Expand Down Expand Up @@ -95,6 +100,8 @@ LLVMTargetMachine::LLVMTargetMachine(const Target &T,

if (EnableTrapUnreachable)
this->Options.TrapUnreachable = true;
if (EnableNoTrapAfterNoreturn)
this->Options.NoTrapAfterNoreturn = true;
}

TargetTransformInfo
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34 changes: 31 additions & 3 deletions llvm/test/CodeGen/ARM/trap-unreachable.ll
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@@ -1,8 +1,36 @@
; RUN: llc -mtriple=thumbv7 -trap-unreachable < %s | FileCheck %s
; CHECK: .inst.n 0xdefe
; RUN: llc -mtriple=thumbv7 -trap-unreachable < %s | FileCheck %s --check-prefixes CHECK,TRAP_UNREACHABLE
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Can you please use update_llc_test_checks.py for this test.

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I used it to generate the test originally, but had to hand-edit it because it produced this output:

...
define void @test_ntanr_noreturn() {
; TRAP_UNREACHABLE-LABEL: test_ntanr_noreturn:
; TRAP_UNREACHABLE:       @ %bb.0:
; TRAP_UNREACHABLE-NEXT:    push {r7, lr}
; TRAP_UNREACHABLE-NEXT:    bl no_return
; TRAP_UNREACHABLE-NEXT:    .inst.n 0xdefe
;
; NTANR-LABEL: test_ntanr_noreturn:
; NTANR:       @ %bb.0:
; NTANR-NEXT:    push {r7, lr}
; NTANR-NEXT:    bl no_return
  call void @no_return()
  unreachable
}

This is a bad test, because it wouldn't reject when --no-trap-after-noreturn doesn't do its job and a trap is still emitted at the end.

This was something that I came across in the other pull request too: update_llc_test_checks.py isn't very good at checking for extraneous instructions at the end of functions.

; RUN: llc -mtriple=thumbv7 -trap-unreachable -no-trap-after-noreturn < %s | FileCheck %s --check-prefixes CHECK,NTANR

define void @test() #0 {
define void @test_trap_unreachable() #0 {
; CHECK-LABEL: test_trap_unreachable:
; CHECK: @ %bb.0:
; CHECK-NEXT: .inst.n 0xdefe
unreachable
}

attributes #0 = { nounwind }

declare void @no_return() noreturn
declare void @could_return()

define void @test_ntanr_noreturn() {
; CHECK-LABEL: test_ntanr_noreturn:
; CHECK: @ %bb.0:
; CHECK-NEXT: push {r7, lr}
; CHECK-NEXT: bl no_return
; TRAP_UNREACHABLE-NEXT: .inst.n 0xdefe
; NTANR-NOT: .inst.n 0xdefe
;
call void @no_return()
unreachable
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I'd suggest adding another block to this function with a non-noreturn call.

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I've added a new function instead, because I thought that was simpler. It makes sure --no-trap-after-noreturn isn't removing traps after normal function call, hopefully that's what you were getting at.

}

define void @test_ntanr_could_return() {
; CHECK-LABEL: test_ntanr_could_return:
; CHECK: @ %bb.0:
; CHECK-NEXT: push {r7, lr}
; CHECK-NEXT: bl could_return
; CHECK-NEXT: .inst.n 0xdefe
call void @could_return()
unreachable
}