[llvm-branch-commits] [llvm] 654c0d8 - Revert "[BranchFolding] Kill common hoisted debug instructions (#140091)"
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llvm-branch-commits at lists.llvm.org
Mon Jul 21 09:24:14 PDT 2025
Author: Orlando Cazalet-Hyams
Date: 2025-07-21T17:24:11+01:00
New Revision: 654c0d846e5e3af60177aff3219e6d501edc6d44
URL: https://github.com/llvm/llvm-project/commit/654c0d846e5e3af60177aff3219e6d501edc6d44
DIFF: https://github.com/llvm/llvm-project/commit/654c0d846e5e3af60177aff3219e6d501edc6d44.diff
LOG: Revert "[BranchFolding] Kill common hoisted debug instructions (#140091)"
This reverts commit 8ba341eec3929dd26679092196cd45dfdd1e60c6.
Added:
Modified:
llvm/lib/CodeGen/BranchFolding.cpp
llvm/test/DebugInfo/X86/branch-folder-dbg.mir
Removed:
################################################################################
diff --git a/llvm/lib/CodeGen/BranchFolding.cpp b/llvm/lib/CodeGen/BranchFolding.cpp
index c1e9a20328527..3b3e7a418feb5 100644
--- a/llvm/lib/CodeGen/BranchFolding.cpp
+++ b/llvm/lib/CodeGen/BranchFolding.cpp
@@ -2083,54 +2083,22 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
if (TBB == FBB) {
MBB->splice(Loc, TBB, TBB->begin(), TIB);
} else {
- // Merge the debug locations, and hoist and kill the debug instructions from
- // both branches. FIXME: We could probably try harder to preserve some debug
- // instructions (but at least this isn't producing wrong locations).
- MachineInstrBuilder MIRBuilder(*MBB->getParent(), Loc);
- auto HoistAndKillDbgInstr = [MBB, Loc](MachineBasicBlock::iterator DI) {
- assert(DI->isDebugInstr() && "Expected a debug instruction");
- if (DI->isDebugRef()) {
- const TargetInstrInfo *TII =
- MBB->getParent()->getSubtarget().getInstrInfo();
- const MCInstrDesc &DBGV = TII->get(TargetOpcode::DBG_VALUE);
- DI = BuildMI(*MBB->getParent(), DI->getDebugLoc(), DBGV, false, 0,
- DI->getDebugVariable(), DI->getDebugExpression());
- MBB->insert(Loc, &*DI);
- return;
- }
-
- DI->setDebugValueUndef();
- DI->moveBefore(&*Loc);
- };
-
// TIB and FIB point to the end of the regions to hoist/merge in TBB and
// FBB.
MachineBasicBlock::iterator FE = FIB;
MachineBasicBlock::iterator FI = FBB->begin();
for (MachineBasicBlock::iterator TI :
make_early_inc_range(make_range(TBB->begin(), TIB))) {
- // Hoist and kill debug instructions from FBB. After this loop FI points
- // to the next non-debug instruction to hoist (checked in assert after the
- // TBB debug instruction handling code).
- while (FI->isDebugInstr()) {
- assert(FI != FE && "Unexpected end of FBB range");
- MachineBasicBlock::iterator FINext = std::next(FI);
- HoistAndKillDbgInstr(FI);
- FI = FINext;
- }
-
- // Kill debug instructions before moving.
- if (TI->isDebugInstr()) {
- HoistAndKillDbgInstr(TI);
+ // Move debug instructions and pseudo probes without modifying them.
+ // FIXME: This is the wrong thing to do for debug locations, which
+ // should at least be killed (and hoisted from BOTH blocks).
+ if (TI->isDebugOrPseudoInstr()) {
+ TI->moveBefore(&*Loc);
continue;
}
- // If FI is a debug instruction, skip forward to the next non-debug
- // instruction.
+ // Get the next non-meta instruction in FBB.
FI = skipDebugInstructionsForward(FI, FE, false);
- // Pseudo probes are excluded from the range when identifying foldable
- // instructions, so we don't expect to see one now.
- assert(!TI->isPseudoProbe() && "Unexpected pseudo probe in range");
// NOTE: The loop above checks CheckKillDead but we can't do that here as
// it modifies some kill markers after the check.
assert(TI->isIdenticalTo(*FI, MachineInstr::CheckDefs) &&
@@ -2143,7 +2111,6 @@ bool BranchFolder::HoistCommonCodeInSuccs(MachineBasicBlock *MBB) {
++FI;
}
}
-
FBB->erase(FBB->begin(), FIB);
if (UpdateLiveIns)
diff --git a/llvm/test/DebugInfo/X86/branch-folder-dbg.mir b/llvm/test/DebugInfo/X86/branch-folder-dbg.mir
index 831b263fdccd4..5c38fd2a43829 100644
--- a/llvm/test/DebugInfo/X86/branch-folder-dbg.mir
+++ b/llvm/test/DebugInfo/X86/branch-folder-dbg.mir
@@ -1,21 +1,16 @@
# RUN: llc %s --start-before=branch-folder --stop-after=branch-folder -o - | FileCheck %s
## Check that common instructions hoisted from `if.then` and `if.else` into
-## common pred `entry` get merged debug locations. The debug instructions from
-## both branches should get hoisted and killed.
-##
-## The MIR debug instructions have been modified by hand in order to check they
-## can be killed.
+## common pred `entry` get merged debug locations.
+
+## FIXME: The debug instructions handling here is wrong.
# CHECK: bb.0
# CHECK: CALL64pcrel32 @f, csr_64, implicit $rsp, implicit $ssp, implicit-def $rsp, implicit-def $ssp, implicit-def $rax
-## --- Start splice from bb.2.if.else (and debug instructions from bb.1.if.then) ---
-# CHECK-NEXT: DBG_VALUE $noreg, $noreg, ![[#]], !DIExpression(), debug-location ![[#]]
-# CHECK-NEXT: DBG_VALUE $noreg, $noreg, ![[#]], !DIExpression(), debug-location ![[#]]
-# CHECK-NEXT: $edi = MOV32r0 implicit-def dead $eflags, debug-instr-number 2, debug-location !DILocation(line: 0, scope: ![[#]])
-# CHECK-NEXT: DBG_VALUE $noreg, $noreg, ![[#]], !DIExpression(DW_OP_LLVM_arg, 0), debug-location ![[#]]
-# CHECK-NEXT: DBG_VALUE $noreg, $noreg, ![[#]], !DIExpression(DW_OP_LLVM_arg, 0), debug-location ![[#]]
-## --- End splice ------------------------------------------------------------------
+## --- Start splice from bb.2.if.else ---
+# CHECK-NEXT: DBG_VALUE 2, $noreg, ![[#]], !DIExpression(), debug-location ![[#]]
+# CHECK-NEXT: $edi = MOV32r0 implicit-def dead $eflags, debug-location !DILocation(line: 0, scope: ![[#]])
+## --- End splice --------------
# CHECK-NEXT: TEST64rr killed renamable $rax, renamable $rax, implicit-def $eflags
# CHECK-NEXT: JCC_1 %bb.2, 9, implicit killed $eflags
# CHECK: bb.1
@@ -78,8 +73,6 @@
...
---
name: g
-tracksRegLiveness: true
-isSSA: false
body: |
bb.0 (%ir-block.0):
successors: %bb.1(0x40000000), %bb.2(0x40000000)
@@ -93,21 +86,22 @@ body: |
bb.1.if.then:
successors: %bb.3(0x80000000)
- DBG_VALUE $esi, $noreg, !11, !DIExpression(), debug-location !13
- $edi = MOV32r0 implicit-def dead $eflags, debug-instr-number 1, debug-location !14
- DBG_INSTR_REF !11, !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref(1, 0), debug-location !13
+
+ DBG_VALUE 0, $noreg, !11, !DIExpression(), debug-location !13
+ $edi = MOV32r0 implicit-def dead $eflags, debug-location !14
$esi = MOV32r0 implicit-def dead $eflags, debug-location !14
CALL64pcrel32 target-flags(x86-plt) @_Z3fooii, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit killed $esi, implicit-def $rsp, implicit-def $ssp, debug-location !14
+ DBG_VALUE 1, $noreg, !11, !DIExpression(), debug-location !13
JMP_1 %bb.3, debug-location !15
bb.2.if.else:
successors: %bb.3(0x80000000)
- DBG_VALUE $esp, $noreg, !11, !DIExpression(), debug-location !13
- $edi = MOV32r0 implicit-def dead $eflags, debug-instr-number 2, debug-location !16
- DBG_INSTR_REF !11, !DIExpression(DW_OP_LLVM_arg, 0), dbg-instr-ref(2, 0), debug-location !13
+ DBG_VALUE 2, $noreg, !11, !DIExpression(), debug-location !13
+ $edi = MOV32r0 implicit-def dead $eflags, debug-location !16
$esi = MOV32ri 1, debug-location !16
CALL64pcrel32 target-flags(x86-plt) @_Z3barii, csr_64, implicit $rsp, implicit $ssp, implicit killed $edi, implicit killed $esi, implicit-def $rsp, implicit-def $ssp, debug-location !16
+ DBG_VALUE 3, $noreg, !11, !DIExpression(), debug-location !13
bb.3.if.end:
$eax = MOV32ri 2
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