[llvm] df2213f - [EHStreamer] Omit @LPStart when function has no landing pads
Rahman Lavaee via llvm-commits
llvm-commits at lists.llvm.org
Mon Aug 15 17:09:56 PDT 2022
Author: Rahman Lavaee
Date: 2022-08-15T17:09:46-07:00
New Revision: df2213f345475786731a2c3b2a121329f14e8950
URL: https://github.com/llvm/llvm-project/commit/df2213f345475786731a2c3b2a121329f14e8950
DIFF: https://github.com/llvm/llvm-project/commit/df2213f345475786731a2c3b2a121329f14e8950.diff
LOG: [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
Added:
llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll
Modified:
llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp b/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
index 31644959bdcae..07a2efaf9383a 100644
--- a/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
+++ b/llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
@@ -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
diff --git a/llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll b/llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll
new file mode 100644
index 0000000000000..96adffc8e0a6f
--- /dev/null
+++ b/llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll
@@ -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:
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