Marge Bot pushed to branch master at Glasgow Haskell Compiler / GHC

Commits:

• 2823b039
  by Ian Duncan at 2026-03-26T03:52:21-04:00

  AArch64: fix MOVK regUsageOfInstr to mark dst as both read and written
  
  MOVK (move with keep) modifies only a 16-bit slice of the destination
  register, so the destination is both read and written. The register
  allocator must know this to avoid clobbering live values. Update
  regUsageOfInstr to list the destination in both src and dst sets.
  
  No regression test: triggering the misallocation requires specific
  register pressure around a MOVK sequence, which is difficult to
  reliably provoke from Haskell source.
  

1 changed file:

• compiler/GHC/CmmToAsm/AArch64/Instr.hs

Changes:

   LSL dst src1 src2        -> usage (regOp src1 ++ regOp src2, regOp dst)

   LSR dst src1 src2        -> usage (regOp src1 ++ regOp src2, regOp dst)

   MOV dst src              -> usage (regOp src, regOp dst)

-  MOVK dst src             -> usage (regOp src, regOp dst)

+  MOVK dst src             -> usage (regOp src ++ regOp dst, regOp dst)

   MOVZ dst src             -> usage (regOp src, regOp dst)

   MVN dst src              -> usage (regOp src, regOp dst)

   ORR _fmt dst src1 src2   -> usage (regOp src1 ++ regOp src2, regOp dst)