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[EHStreamer] Omit @LPStart when function has no landing pads 

When no landing pads exist for a function, `@LPStart` is undefined and must be omitted.

EH table is generally not emitted for functions without landing pads, except when the personality function is uknown (`!isNoOpWithoutInvoke(classifyEHPersonality(Per))`). In that case, we must omit `@LPStart` even when machine function splitting is enabled.

Reviewed By: MaskRay

Differential Revision: https://reviews.llvm.org/D131626
This commit is contained in:
Rahman Lavaee 2022-08-10 14:43:06 -07:00
parent 65c022a75f
commit df2213f345
2 changed files with 48 additions and 3 deletions
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7
llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
View File

@ -663,9 +663,10 @@ MCSymbol *EHStreamer::emitExceptionTable() {
Asm->OutStreamer->emitLabel(CSRange.ExceptionLabel);
// Emit the LSDA header.
// If only one call-site range exists, LPStart is omitted as it is the
// same as the function entry.
if (CallSiteRanges.size() == 1) {
// LPStart is omitted if either we have a single call-site range (in which
// case the function entry is treated as @LPStart) or if this function has
// no landing pads (in which case @LPStart is undefined).
if (CallSiteRanges.size() == 1 || LandingPadRange == nullptr) {
Asm->emitEncodingByte(dwarf::DW_EH_PE_omit, "@LPStart");
} else if (!Asm->isPositionIndependent()) {
// For more than one call-site ranges, LPStart must be explicitly

44
llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll Normal file
View File

@ -0,0 +1,44 @@
;; Verify that @LPStart is omitted when there are no landing pads. This test
;; uses an unkown personality to force emitting the exception table.
; RUN: llc -basic-block-sections=all -mtriple=x86_64 < %s | FileCheck %s
declare void @throwit()
declare i32 @__unknown_ehpersonality(...)
define void @foo(i1 %cond) uwtable personality ptr @__unknown_ehpersonality {
entry:
br i1 %cond, label %cond.true, label %cond.false
cond.true: ; preds = %entry
call void @throwit()
unreachable
cond.false: ; preds = %entry
ret void
}
; CHECK: GCC_except_table0:
; CHECK-NEXT: .Lexception0:
; CHECK-NEXT: .byte 255 # @LPStart Encoding = omit
; CHECK-NEXT: .byte 255 # @TType Encoding = omit
; CHECK-NEXT: .byte 1 # Call site Encoding = uleb128
; CHECK-NEXT: .uleb128 .Laction_table_base0-.Lcst_begin0
; CHECK-NEXT: .Lcst_begin0:
; CHECK-NEXT: .Lexception1:
; CHECK-NEXT: .byte 255 # @LPStart Encoding = omit
; CHECK-NEXT: .byte 255 # @TType Encoding = omit
; CHECK-NEXT: .byte 1 # Call site Encoding = uleb128
; CHECK-NEXT: .uleb128 .Laction_table_base0-.Lcst_begin1
; CHECK-NEXT: .Lcst_begin1:
; CHECK-NEXT: .Lexception2:
; CHECK-NEXT: .byte 255 # @LPStart Encoding = omit
; CHECK-NEXT: .byte 255 # @TType Encoding = omit
; CHECK-NEXT: .byte 1 # Call site Encoding = uleb128
; CHECK-NEXT: .uleb128 .Laction_table_base0-.Lcst_begin2
; CHECK-NEXT: .Lcst_begin2:
; CHECK-NEXT: .uleb128 foo.__part.2-foo.__part.2 # >> Call Site 1 <<
; CHECK-NEXT: .uleb128 .LBB_END0_2-foo.__part.2 # Call between foo.__part.2 and .LBB_END0_2
; CHECK-NEXT: .byte 0 # has no landing pad
; CHECK-NEXT: .byte 0 # On action: cleanup
; CHECK-NEXT: .Laction_table_base0: