[llvm] [MC] Don't treat altentry symbols as atoms (PR #97479)
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Tue Jul 2 13:55:26 PDT 2024
llvmbot wrote:
<!--LLVM PR SUMMARY COMMENT-->
@llvm/pr-subscribers-mc
Author: Fangrui Song (MaskRay)
<details>
<summary>Changes</summary>
The current `setAtom` is inaccurate: a `.alt_entry` label can also be
recognized as an atom. This is mostly benign, but might cause two
locations only separated by an `.alt_entry` to have different atoms.
The `evaluateAsAbsolute` code added by https://reviews.llvm.org/D153167
would not fold `A-B` when they are only separated by a `.alt_entry`
label, leading to a spurious error.
The fix is similar to #<!-- -->82268: add a special case for `.alt_entry`.
Fix #<!-- -->97116
---
Full diff: https://github.com/llvm/llvm-project/pull/97479.diff
2 Files Affected:
- (modified) llvm/lib/MC/MCMachOStreamer.cpp (+1-1)
- (modified) llvm/test/MC/MachO/cfi-advance-loc-err.s (+5)
``````````diff
diff --git a/llvm/lib/MC/MCMachOStreamer.cpp b/llvm/lib/MC/MCMachOStreamer.cpp
index d67b95820a8a9..0b34d87033b7b 100644
--- a/llvm/lib/MC/MCMachOStreamer.cpp
+++ b/llvm/lib/MC/MCMachOStreamer.cpp
@@ -508,7 +508,7 @@ void MCMachOStreamer::finishImpl() {
DenseMap<const MCFragment *, const MCSymbol *> DefiningSymbolMap;
for (const MCSymbol &Symbol : getAssembler().symbols()) {
if (getAssembler().isSymbolLinkerVisible(Symbol) && Symbol.isInSection() &&
- !Symbol.isVariable()) {
+ !Symbol.isVariable() && !cast<MCSymbolMachO>(Symbol).isAltEntry()) {
// An atom defining symbol should never be internal to a fragment.
assert(Symbol.getOffset() == 0 &&
"Invalid offset in atom defining symbol!");
diff --git a/llvm/test/MC/MachO/cfi-advance-loc-err.s b/llvm/test/MC/MachO/cfi-advance-loc-err.s
index 3143dd84efc63..77b6544cb12d8 100644
--- a/llvm/test/MC/MachO/cfi-advance-loc-err.s
+++ b/llvm/test/MC/MachO/cfi-advance-loc-err.s
@@ -9,6 +9,11 @@ _foo:
subq $8, %rsp
.cfi_adjust_cfa_offset 8
+ .alt_entry _bar
+_bar: # alt_entry label can appear here as it is not an atom
+ addq $8, %rsp
+ .cfi_adjust_cfa_offset -8
+
tmp0: # non-private label cannot appear here
addq $8, %rsp
# CHECK: :[[#@LINE+1]]:3: error: invalid CFI advance_loc expression
``````````
</details>
https://github.com/llvm/llvm-project/pull/97479
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