[llvm] [LiveIntervals] repairIntervalsInRange: recompute width changes (PR #78564)

[Carl Ritson via llvm-commits]

https://github.com/perlfu created https://github.com/llvm/llvm-project/pull/78564

Extend repairIntervalsInRange to completely recompute the interva for a register if subregister defs exist without precise subrange matches (LaneMask exactly matching subregister).
This occurs when register sequences are lowered to copies such that the size of the copies do not match any uses of the subregisters formed (i.e. during twoaddressinstruction).

The subranges without this change are probably legal, but do not match those generated by live interval computation.  This creates problems with other code that assumes subranges precisely cover all subregisters defined, e.g. shrinkToUses().

>From abbbd9d369dcbd2f248f55fae3eb964d49f3aec4 Mon Sep 17 00:00:00 2001
From: Carl Ritson <carl.ritson at amd.com>
Date: Thu, 18 Jan 2024 16:53:44 +0900
Subject: [PATCH] [LiveIntervals] repairIntervalsInRange: recompute width
 changes

Extend repairIntervalsInRange to completely recompute the interva
for a register if subregister defs exist without precise subrange
matches (LaneMask exactly matching subregister).
This occurs when register sequences are lowered to copies such
that the size of the copies do not match any uses of the
subregisters formed (i.e. during twoaddressinstruction).

The subranges without this change are probably legal, but do not
match those generated by live interval computation.  This creates
problems with other code that assumes subranges precisely cover
all subregisters defined, e.g. shrinkToUses().
---
 llvm/lib/CodeGen/LiveIntervals.cpp            | 29 +++++++++++++++----
 .../test/CodeGen/AMDGPU/lds-misaligned-bug.ll |  1 +
 2 files changed, 24 insertions(+), 6 deletions(-)

diff --git a/llvm/lib/CodeGen/LiveIntervals.cpp b/llvm/lib/CodeGen/LiveIntervals.cpp
index 68fff9bc221d0b..53693387a3e856 100644
--- a/llvm/lib/CodeGen/LiveIntervals.cpp
+++ b/llvm/lib/CodeGen/LiveIntervals.cpp
@@ -1666,13 +1666,30 @@ LiveIntervals::repairIntervalsInRange(MachineBasicBlock *MBB,
     for (const MachineOperand &MO : MI.operands()) {
       if (MO.isReg() && MO.getReg().isVirtual()) {
         Register Reg = MO.getReg();
-        // If the new instructions refer to subregs but the old instructions did
-        // not, throw away any old live interval so it will be recomputed with
-        // subranges.
         if (MO.getSubReg() && hasInterval(Reg) &&
-            !getInterval(Reg).hasSubRanges() &&
-            MRI->shouldTrackSubRegLiveness(Reg))
-          removeInterval(Reg);
+            MRI->shouldTrackSubRegLiveness(Reg)) {
+          LiveInterval &LI = getInterval(Reg);
+          if (!LI.hasSubRanges()) {
+            // If the new instructions refer to subregs but the old instructions
+            // did not, throw away any old live interval so it will be
+            // recomputed with subranges.
+            removeInterval(Reg);
+          } else if (MO.isDef()) {
+            // Similarly if a subreg def has no precise subrange match then
+            // assume we need to recompute all subranges.
+            unsigned SubReg = MO.getSubReg();
+            LaneBitmask Mask = TRI->getSubRegIndexLaneMask(SubReg);
+            bool hasMatch = false;
+            for (auto &SR : LI.subranges()) {
+              if (SR.LaneMask != Mask)
+                continue;
+              hasMatch = true;
+              break;
+            }
+            if (!hasMatch)
+              removeInterval(Reg);
+          }
+        }
         if (!hasInterval(Reg)) {
           createAndComputeVirtRegInterval(Reg);
           // Don't bother to repair a freshly calculated live interval.
diff --git a/llvm/test/CodeGen/AMDGPU/lds-misaligned-bug.ll b/llvm/test/CodeGen/AMDGPU/lds-misaligned-bug.ll
index 3a8f06ba59a129..01af3346523827 100644
--- a/llvm/test/CodeGen/AMDGPU/lds-misaligned-bug.ll
+++ b/llvm/test/CodeGen/AMDGPU/lds-misaligned-bug.ll
@@ -5,6 +5,7 @@
 ; RUN: llc -mtriple=amdgcn -mcpu=gfx1010 -verify-machineinstrs -mattr=+cumode,+unaligned-access-mode < %s | FileCheck -check-prefixes=GCN,UNALIGNED,VECT %s
 ; RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs < %s | FileCheck -check-prefixes=GCN,ALIGNED,VECT %s
 ; RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs -mattr=+cumode < %s | FileCheck -check-prefixes=GCN,ALIGNED,VECT %s
+; RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs -mattr=+cumode -early-live-intervals < %s | FileCheck -check-prefixes=GCN,ALIGNED,VECT %s
 ; RUN: llc -mtriple=amdgcn -mcpu=gfx1100 -verify-machineinstrs -mattr=+cumode,+unaligned-access-mode < %s | FileCheck -check-prefixes=GCN,UNALIGNED,VECT %s
 
 ; GCN-LABEL: test_local_misaligned_v2: