[llvm] 0ea5eb1 - [RegisterCoalescer] Fix updating LiveIntervals in joinReservedPhysReg

[Jay Foad via llvm-commits]

Author: Jay Foad
Date: 2023-05-24T15:19:05+01:00
New Revision: 0ea5eb143c7a63105b4479c455642b4c4ef3278c

URL: https://github.com/llvm/llvm-project/commit/0ea5eb143c7a63105b4479c455642b4c4ef3278c
DIFF: https://github.com/llvm/llvm-project/commit/0ea5eb143c7a63105b4479c455642b4c4ef3278c.diff

LOG: [RegisterCoalescer] Fix updating LiveIntervals in joinReservedPhysReg

Live intervals for physical registers are calculated lazily on demand.
In a case like this:

  16B    %0:gpr32 = IMPLICIT_DEF
  32B    $wzr = COPY %0

if the live interval for $wzr did not already exist then the update code
in joinReservedPhysReg would create it with a definition at 32B, which
would remain even after the COPY was deleted.

Differential Revision: https://reviews.llvm.org/D151314

Added: 
    

Modified: 
    llvm/lib/CodeGen/RegisterCoalescer.cpp
    llvm/test/CodeGen/AArch64/regcoal-physreg.mir

Removed: 
    


################################################################################
diff  --git a/llvm/lib/CodeGen/RegisterCoalescer.cpp b/llvm/lib/CodeGen/RegisterCoalescer.cpp
index f72d0d50f4709..87a4ace6cb34d 100644
--- a/llvm/lib/CodeGen/RegisterCoalescer.cpp
+++ b/llvm/lib/CodeGen/RegisterCoalescer.cpp
@@ -2196,6 +2196,7 @@ bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
     //   ...
     //   use %physreg_x
     CopyMI = MRI->getVRegDef(SrcReg);
+    deleteInstr(CopyMI);
   } else {
     // VReg is copied into physreg:
     //   %y = def
@@ -2240,6 +2241,8 @@ bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
                       << printReg(DstReg, TRI) << " at " << CopyRegIdx << "\n");
 
     LIS->removePhysRegDefAt(DstReg.asMCReg(), CopyRegIdx);
+    deleteInstr(CopyMI);
+
     // Create a new dead def at the new def location.
     for (MCRegUnitIterator UI(DstReg, TRI); UI.isValid(); ++UI) {
       LiveRange &LR = LIS->getRegUnit(*UI);
@@ -2247,8 +2250,6 @@ bool RegisterCoalescer::joinReservedPhysReg(CoalescerPair &CP) {
     }
   }
 
-  deleteInstr(CopyMI);
-
   // We don't track kills for reserved registers.
   MRI->clearKillFlags(CP.getSrcReg());
 

diff  --git a/llvm/test/CodeGen/AArch64/regcoal-physreg.mir b/llvm/test/CodeGen/AArch64/regcoal-physreg.mir
index 270abeec822c0..05b66de3d0c34 100644
--- a/llvm/test/CodeGen/AArch64/regcoal-physreg.mir
+++ b/llvm/test/CodeGen/AArch64/regcoal-physreg.mir
@@ -1,4 +1,8 @@
-# RUN: llc -mtriple=aarch64-apple-ios -run-pass=simple-register-coalescing -verify-machineinstrs %s -o - | FileCheck %s
+# RUN: llc -mtriple=aarch64-apple-ios -run-pass=simple-register-coalescing,simple-register-coalescing -verify-machineinstrs %s -o - | FileCheck %s
+
+# FIXME: Second run of the pass is a workaround for a bug in
+# -run-pass. The verifier doesn't detect broken LiveIntervals, see bug
+# 46873
 --- |
   declare void @f2()