diff options
Diffstat (limited to 'compiler/nativeGen/X86/CodeGen.hs')
| -rw-r--r-- | compiler/nativeGen/X86/CodeGen.hs | 28 |
1 files changed, 21 insertions, 7 deletions
diff --git a/compiler/nativeGen/X86/CodeGen.hs b/compiler/nativeGen/X86/CodeGen.hs index 8cea28d920..616c23a657 100644 --- a/compiler/nativeGen/X86/CodeGen.hs +++ b/compiler/nativeGen/X86/CodeGen.hs @@ -180,11 +180,16 @@ verifyBasicBlock instrs CALL {} | atEnd -> faultyBlockWith i | not atEnd -> go atEnd instr -- All instructions ok, check if we reached the end and continue. - _ | not atEnd -> go (isJumpishInstr i) instr - -- Only jumps allowed at the end of basic blocks. - | otherwise -> if isJumpishInstr i - then go True instr - else faultyBlockWith i + _ | not atEnd -> go (isJumpishInstr i) instr + | isTerminalInstr i -> go True instr + | otherwise -> faultyBlockWith i + + -- Only jumps (or UD2, which always follows indirect jumps) + -- allowed at the end of basic blocks. + isTerminalInstr UD2 = True + isTerminalInstr i | isJumpishInstr i = True + isTerminalInstr _ = False + faultyBlockWith i = pprPanic "Non control flow instructions after end of basic block." (ppr i <+> text "in:" $$ vcat (map ppr instrs)) @@ -1766,19 +1771,28 @@ assignReg_FltCode _ reg src = do let platform = targetPlatform dflags return (src_code (getRegisterReg platform reg)) +-- Note [UD2 after indirect jumps] +-- ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ +-- +-- We follow all indirect jumps with a UD2 instruction to ensure that the +-- instruction decoder doesn't attempt to decode the fallthrough path, which +-- can result in resource conflicts. See Intel Software Optimisation Manual +-- Section 3.4.1.6 (Branch Type Selection), Rule 14. genJump :: CmmExpr{-the branch target-} -> [Reg] -> NatM InstrBlock genJump (CmmLoad mem _) regs = do Amode target code <- getAmode mem - return (code `snocOL` JMP (OpAddr target) regs) + -- See Note [UD2 after indirect jumps] + return (code `snocOL` JMP (OpAddr target) regs `snocOL` UD2) genJump (CmmLit lit) regs = do return (unitOL (JMP (OpImm (litToImm lit)) regs)) genJump expr regs = do (reg,code) <- getSomeReg expr - return (code `snocOL` JMP (OpReg reg) regs) + -- See Note [UD2 after indirect jumps] + return (code `snocOL` JMP (OpReg reg) regs `snocOL` UD2) -- ----------------------------------------------------------------------------- |