[PATCH] D131626: [EHStreamer] Omit @LPStart when function has no landing pads

[Rahman Lavaee via Phabricator via llvm-commits]

rahmanl updated this revision to Diff 451950.
rahmanl added a comment.

Revised the comment.


Repository:
  rG LLVM Github Monorepo

CHANGES SINCE LAST ACTION
  https://reviews.llvm.org/D131626/new/

https://reviews.llvm.org/D131626

Files:
  llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
  llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll


Index: llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll
===================================================================
--- /dev/null
+++ llvm/test/CodeGen/X86/gcc_except_table_bb_sections_nolpads.ll
@@ -0,0 +1,27 @@
+;; 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 -code-model=small < %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:      .Lexception1:
+; CHECK-NEXT:    .byte   255                             # @LPStart Encoding = omit
+; CHECK:      .Lexception2:
+; CHECK-NEXT:    .byte   255                             # @LPStart Encoding = omit
Index: llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
===================================================================
--- llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
+++ llvm/lib/CodeGen/AsmPrinter/EHStreamer.cpp
@@ -663,9 +663,10 @@
       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


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