Add a "clobbers_flags" flag to encoding recipes.

On some ISAs like Intel's, all arithmetic instructions set all or some
of the CPU flags, so flag values can't be live across these
instructions. On ISAs like ARM's Aarch32, flags are clobbered by compact
16-bit encodings but not necessarily by 32-bit encodings of the same
instruction.

The "clobbers_flags" bit on the encoding recipe is used to indicate if
CPU flag values can be live across an instruction, or conversely whether
the encoding can be used where flag values are live.

lib/cretonne/meta/cdsl/isa.py

@@ -310,16 +310,21 @@ class EncRecipe(object):
     branch instructions. It is an `(origin, bits)` tuple describing the exact
     range that can be encoded in a branch instruction.
 
+    For ISAs that use CPU flags in `iflags` and `fflags` value types, the
+    `clobbers_flags` is used to indicate instruction encodings that clobbers
+    the CPU flags, so they can't be used where a flag value is live.
+
     :param name: Short mnemonic name for this recipe.
     :param format: All encoded instructions must have this
             :py:class:`InstructionFormat`.
     :param size: Number of bytes in the binary encoded instruction.
-    :param: ins Tuple of register constraints for value operands.
-    :param: outs Tuple of register constraints for results.
-    :param: branch_range `(origin, bits)` range for branches.
-    :param: instp Instruction predicate.
-    :param: isap ISA predicate.
-    :param: emit Rust code for binary emission.
+    :param ins: Tuple of register constraints for value operands.
+    :param outs: Tuple of register constraints for results.
+    :param branch_range: `(origin, bits)` range for branches.
+    :param clobbers_flags: This instruction clobbers `iflags` and `fflags`.
+    :param instp: Instruction predicate.
+    :param isap: ISA predicate.
+    :param emit: Rust code for binary emission.
     """
 
     def __init__(
@@ -330,6 +335,7 @@ class EncRecipe(object):
             ins,                  # type: ConstraintSeq
             outs,                 # type: ConstraintSeq
             branch_range=None,    # type: BranchRange
+            clobbers_flags=True,  # type: bool
             instp=None,           # type: PredNode
             isap=None,            # type: PredNode
             emit=None             # type: str
@@ -340,6 +346,7 @@ class EncRecipe(object):
         assert size >= 0
         self.size = size
         self.branch_range = branch_range
+        self.clobbers_flags = clobbers_flags
         self.instp = instp
         self.isap = isap
         self.emit = emit

lib/cretonne/meta/gen_encoding.py

@@ -766,6 +766,9 @@ def emit_recipe_constraints(isa, fmt):
                         str(any(isinstance(c, Register)
                             for c in r.outs)).lower())
                 fmt.format('tied_ops: {},', str(bool(tied_i2o)).lower())
+                fmt.format(
+                        'clobbers_flags: {},',
+                        str(bool(r.clobbers_flags)).lower())
 
 
 def emit_operand_constraints(

lib/cretonne/meta/isa/intel/recipes.py

@@ -147,6 +147,7 @@ class TailRecipe:
             ins,                    # type: ConstraintSeq
             outs,                   # type: ConstraintSeq
             branch_range=None,      # type: int
+            clobbers_flags=True,    # type: bool
             instp=None,             # type: PredNode
             isap=None,              # type: PredNode
             when_prefixed=None,     # type: TailRecipe
@@ -160,6 +161,7 @@ class TailRecipe:
         self.ins = ins
         self.outs = outs
         self.branch_range = branch_range
+        self.clobbers_flags = clobbers_flags
         self.instp = instp
         self.isap = isap
         self.when_prefixed = when_prefixed
@@ -194,6 +196,7 @@ class TailRecipe:
                 ins=self.ins,
                 outs=self.outs,
                 branch_range=branch_range,
+                clobbers_flags=self.clobbers_flags,
                 instp=self.instp,
                 isap=self.isap,
                 emit=replace_put_op(self.emit, name))
@@ -236,6 +239,7 @@ class TailRecipe:
                 ins=self.ins,
                 outs=self.outs,
                 branch_range=branch_range,
+                clobbers_flags=self.clobbers_flags,
                 instp=self.instp,
                 isap=self.isap,
                 emit=replace_put_op(self.emit, name))
@@ -302,9 +306,10 @@ fax = TailRecipe(
         ''')
 
 # XX /r, but for a unary operator with separate input/output register, like
-# copies. MR form.
+# copies. MR form, preserving flags.
 umr = TailRecipe(
         'umr', Unary, size=1, ins=GPR, outs=GPR,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(out_reg0, in_reg0), sink);
         modrm_rr(out_reg0, in_reg0, sink);
@@ -313,6 +318,7 @@ umr = TailRecipe(
 # Same as umr, but with FPR -> GPR registers.
 rfumr = TailRecipe(
         'rfumr', Unary, size=1, ins=FPR, outs=GPR,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(out_reg0, in_reg0), sink);
         modrm_rr(out_reg0, in_reg0, sink);
@@ -339,6 +345,7 @@ urm_abcd = TailRecipe(
 # XX /r, RM form, FPR -> FPR.
 furm = TailRecipe(
         'furm', Unary, size=1, ins=FPR, outs=FPR,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_rr(in_reg0, out_reg0, sink);
@@ -347,6 +354,7 @@ furm = TailRecipe(
 # XX /r, RM form, GPR -> FPR.
 frurm = TailRecipe(
         'frurm', Unary, size=1, ins=GPR, outs=FPR,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_rr(in_reg0, out_reg0, sink);
@@ -355,6 +363,7 @@ frurm = TailRecipe(
 # XX /r, RM form, FPR -> GPR.
 rfurm = TailRecipe(
         'rfurm', Unary, size=1, ins=FPR, outs=GPR,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_rr(in_reg0, out_reg0, sink);
@@ -378,6 +387,7 @@ furmi_rnd = TailRecipe(
 # XX /r, for regmove instructions.
 rmov = TailRecipe(
         'rmov', RegMove, size=1, ins=GPR, outs=(),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(dst, src), sink);
         modrm_rr(dst, src, sink);
@@ -386,6 +396,7 @@ rmov = TailRecipe(
 # XX /r, for regmove instructions (FPR version, RM encoded).
 frmov = TailRecipe(
         'frmov', RegMove, size=1, ins=FPR, outs=(),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(src, dst), sink);
         modrm_rr(src, dst, sink);
@@ -489,6 +500,7 @@ fnaddr8 = TailRecipe(
 st = TailRecipe(
         'st', Store, size=1, ins=(GPR, GPR), outs=(),
         instp=IsEqual(Store.offset, 0),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_rm(in_reg1, in_reg0, sink);
@@ -500,6 +512,7 @@ st_abcd = TailRecipe(
         'st_abcd', Store, size=1, ins=(ABCD, GPR), outs=(),
         instp=IsEqual(Store.offset, 0),
         when_prefixed=st,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_rm(in_reg1, in_reg0, sink);
@@ -509,6 +522,7 @@ st_abcd = TailRecipe(
 fst = TailRecipe(
         'fst', Store, size=1, ins=(FPR, GPR), outs=(),
         instp=IsEqual(Store.offset, 0),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_rm(in_reg1, in_reg0, sink);
@@ -518,6 +532,7 @@ fst = TailRecipe(
 stDisp8 = TailRecipe(
         'stDisp8', Store, size=2, ins=(GPR, GPR), outs=(),
         instp=IsSignedInt(Store.offset, 8),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_disp8(in_reg1, in_reg0, sink);
@@ -528,6 +543,7 @@ stDisp8_abcd = TailRecipe(
         'stDisp8_abcd', Store, size=2, ins=(ABCD, GPR), outs=(),
         instp=IsSignedInt(Store.offset, 8),
         when_prefixed=stDisp8,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_disp8(in_reg1, in_reg0, sink);
@@ -537,6 +553,7 @@ stDisp8_abcd = TailRecipe(
 fstDisp8 = TailRecipe(
         'fstDisp8', Store, size=2, ins=(FPR, GPR), outs=(),
         instp=IsSignedInt(Store.offset, 8),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_disp8(in_reg1, in_reg0, sink);
@@ -547,6 +564,7 @@ fstDisp8 = TailRecipe(
 # XX /r register-indirect store with 32-bit offset.
 stDisp32 = TailRecipe(
         'stDisp32', Store, size=5, ins=(GPR, GPR), outs=(),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_disp32(in_reg1, in_reg0, sink);
@@ -556,6 +574,7 @@ stDisp32 = TailRecipe(
 stDisp32_abcd = TailRecipe(
         'stDisp32_abcd', Store, size=5, ins=(ABCD, GPR), outs=(),
         when_prefixed=stDisp32,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_disp32(in_reg1, in_reg0, sink);
@@ -564,6 +583,7 @@ stDisp32_abcd = TailRecipe(
         ''')
 fstDisp32 = TailRecipe(
         'fstDisp32', Store, size=5, ins=(FPR, GPR), outs=(),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg1, in_reg0), sink);
         modrm_disp32(in_reg1, in_reg0, sink);
@@ -574,6 +594,7 @@ fstDisp32 = TailRecipe(
 # Unary spill with SIB and 32-bit displacement.
 spSib32 = TailRecipe(
         'spSib32', Unary, size=6, ins=GPR, outs=StackGPR32,
+        clobbers_flags=False,
         emit='''
         let base = stk_base(out_stk0.base);
         PUT_OP(bits, rex2(base, in_reg0), sink);
@@ -583,6 +604,7 @@ spSib32 = TailRecipe(
         ''')
 fspSib32 = TailRecipe(
         'fspSib32', Unary, size=6, ins=FPR, outs=StackFPR32,
+        clobbers_flags=False,
         emit='''
         let base = stk_base(out_stk0.base);
         PUT_OP(bits, rex2(base, in_reg0), sink);
@@ -594,6 +616,7 @@ fspSib32 = TailRecipe(
 # Regspill using RSP-relative addressing.
 rsp32 = TailRecipe(
         'rsp32', RegSpill, size=6, ins=GPR, outs=(),
+        clobbers_flags=False,
         emit='''
         let dst = StackRef::sp(dst, &func.stack_slots);
         let base = stk_base(dst.base);
@@ -604,6 +627,7 @@ rsp32 = TailRecipe(
         ''')
 frsp32 = TailRecipe(
         'frsp32', RegSpill, size=6, ins=FPR, outs=(),
+        clobbers_flags=False,
         emit='''
         let dst = StackRef::sp(dst, &func.stack_slots);
         let base = stk_base(dst.base);
@@ -621,6 +645,7 @@ frsp32 = TailRecipe(
 ld = TailRecipe(
         'ld', Load, size=1, ins=(GPR), outs=(GPR),
         instp=IsEqual(Load.offset, 0),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_rm(in_reg0, out_reg0, sink);
@@ -630,6 +655,7 @@ ld = TailRecipe(
 fld = TailRecipe(
         'fld', Load, size=1, ins=(GPR), outs=(FPR),
         instp=IsEqual(Load.offset, 0),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_rm(in_reg0, out_reg0, sink);
@@ -639,6 +665,7 @@ fld = TailRecipe(
 ldDisp8 = TailRecipe(
         'ldDisp8', Load, size=2, ins=(GPR), outs=(GPR),
         instp=IsSignedInt(Load.offset, 8),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_disp8(in_reg0, out_reg0, sink);
@@ -650,6 +677,7 @@ ldDisp8 = TailRecipe(
 fldDisp8 = TailRecipe(
         'fldDisp8', Load, size=2, ins=(GPR), outs=(FPR),
         instp=IsSignedInt(Load.offset, 8),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_disp8(in_reg0, out_reg0, sink);
@@ -661,6 +689,7 @@ fldDisp8 = TailRecipe(
 ldDisp32 = TailRecipe(
         'ldDisp32', Load, size=5, ins=(GPR), outs=(GPR),
         instp=IsSignedInt(Load.offset, 32),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_disp32(in_reg0, out_reg0, sink);
@@ -672,6 +701,7 @@ ldDisp32 = TailRecipe(
 fldDisp32 = TailRecipe(
         'fldDisp32', Load, size=5, ins=(GPR), outs=(FPR),
         instp=IsSignedInt(Load.offset, 32),
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, rex2(in_reg0, out_reg0), sink);
         modrm_disp32(in_reg0, out_reg0, sink);
@@ -682,6 +712,7 @@ fldDisp32 = TailRecipe(
 # Unary fill with SIB and 32-bit displacement.
 fiSib32 = TailRecipe(
         'fiSib32', Unary, size=6, ins=StackGPR32, outs=GPR,
+        clobbers_flags=False,
         emit='''
         let base = stk_base(in_stk0.base);
         PUT_OP(bits, rex2(base, out_reg0), sink);
@@ -691,6 +722,7 @@ fiSib32 = TailRecipe(
         ''')
 ffiSib32 = TailRecipe(
         'ffiSib32', Unary, size=6, ins=StackFPR32, outs=FPR,
+        clobbers_flags=False,
         emit='''
         let base = stk_base(in_stk0.base);
         PUT_OP(bits, rex2(base, out_reg0), sink);
@@ -702,6 +734,7 @@ ffiSib32 = TailRecipe(
 # Regfill with RSP-relative 32-bit displacement.
 rfi32 = TailRecipe(
         'rfi32', RegFill, size=6, ins=StackGPR32, outs=(),
+        clobbers_flags=False,
         emit='''
         let src = StackRef::sp(src, &func.stack_slots);
         let base = stk_base(src.base);
@@ -712,6 +745,7 @@ rfi32 = TailRecipe(
         ''')
 frfi32 = TailRecipe(
         'frfi32', RegFill, size=6, ins=StackFPR32, outs=(),
+        clobbers_flags=False,
         emit='''
         let src = StackRef::sp(src, &func.stack_slots);
         let base = stk_base(src.base);
@@ -751,6 +785,7 @@ ret = TailRecipe(
 jmpb = TailRecipe(
         'jmpb', Jump, size=1, ins=(), outs=(),
         branch_range=8,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, BASE_REX, sink);
         disp1(destination, func, sink);
@@ -759,6 +794,7 @@ jmpb = TailRecipe(
 jmpd = TailRecipe(
         'jmpd', Jump, size=4, ins=(), outs=(),
         branch_range=32,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits, BASE_REX, sink);
         disp4(destination, func, sink);
@@ -767,6 +803,7 @@ jmpd = TailRecipe(
 brib = TailRecipe(
         'brib', BranchInt, size=1, ins=FLAG.eflags, outs=(),
         branch_range=8,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits | icc2opc(cond), BASE_REX, sink);
         disp1(destination, func, sink);
@@ -775,6 +812,7 @@ brib = TailRecipe(
 brid = TailRecipe(
         'brid', BranchInt, size=4, ins=FLAG.eflags, outs=(),
         branch_range=32,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits | icc2opc(cond), BASE_REX, sink);
         disp4(destination, func, sink);
@@ -783,6 +821,7 @@ brid = TailRecipe(
 brfb = TailRecipe(
         'brfb', BranchFloat, size=1, ins=FLAG.eflags, outs=(),
         branch_range=8,
+        clobbers_flags=False,
         instp=floatccs(BranchFloat),
         emit='''
         PUT_OP(bits | fcc2opc(cond), BASE_REX, sink);
@@ -792,6 +831,7 @@ brfb = TailRecipe(
 brfd = TailRecipe(
         'brfd', BranchFloat, size=4, ins=FLAG.eflags, outs=(),
         branch_range=32,
+        clobbers_flags=False,
         instp=floatccs(BranchFloat),
         emit='''
         PUT_OP(bits | fcc2opc(cond), BASE_REX, sink);
@@ -811,6 +851,7 @@ brfd = TailRecipe(
 seti = TailRecipe(
         'seti', IntCond, size=1, ins=FLAG.eflags, outs=GPR,
         requires_prefix=True,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits | icc2opc(cond), rex1(out_reg0), sink);
         modrm_r_bits(out_reg0, bits, sink);
@@ -818,6 +859,7 @@ seti = TailRecipe(
 seti_abcd = TailRecipe(
         'seti_abcd', IntCond, size=1, ins=FLAG.eflags, outs=ABCD,
         when_prefixed=seti,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits | icc2opc(cond), rex1(out_reg0), sink);
         modrm_r_bits(out_reg0, bits, sink);
@@ -826,6 +868,7 @@ seti_abcd = TailRecipe(
 setf = TailRecipe(
         'setf', FloatCond, size=1, ins=FLAG.eflags, outs=GPR,
         requires_prefix=True,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits | fcc2opc(cond), rex1(out_reg0), sink);
         modrm_r_bits(out_reg0, bits, sink);
@@ -833,6 +876,7 @@ setf = TailRecipe(
 setf_abcd = TailRecipe(
         'setf_abcd', FloatCond, size=1, ins=FLAG.eflags, outs=ABCD,
         when_prefixed=setf,
+        clobbers_flags=False,
         emit='''
         PUT_OP(bits | fcc2opc(cond), rex1(out_reg0), sink);
         modrm_r_bits(out_reg0, bits, sink);

lib/cretonne/src/isa/constraints.rs

@@ -106,6 +106,11 @@ pub struct RecipeConstraints {
 
     /// Are there any tied operands?
     pub tied_ops: bool,
+
+    /// Does this instruction clobber the CPU flags?
+    ///
+    /// When true, SSA values of type `iflags` or `fflags` can not be live across the instruction.
+    pub clobbers_flags: bool,
 }
 
 impl RecipeConstraints {