Whenever the flags thunk is set, fill in all the fields, even NDEP

which isn't usually used.  This makes redundant-PUT elimination work
better, fixing a rather subtle optimisation bug.  For at least one
floating-point case this gives a significant speedup.  Consider a bb
like this:

    (no flag setting insns before inc)
    inc ...
    (no flag setting insns)
    add ...

inc sets CC_OP, CC_DEP1 and CC_NDEP; the latter is expensive because a
call to calculate_eflags_c is required.

add sets CC_OP, CC_DEP1 and CC_DEP2.  The CC_NDEP value is now
irrelevant, but because CC_NDEP is not overwritten, iropt cannot
remove the previous assignment to it, and so the expensive helper call
remains even though it is irrelevant.

This commit fixes that: By always setting NDEP to zero whenever its
value will be unused, any previous assignment to it will be removed by
iropt.

This change should be propagated to the amd64 front end too.

git-svn-id: svn://svn.valgrind.org/vex/trunk@1119

diff --git a/VEX/priv/guest-x86/toIR.c b/VEX/priv/guest-x86/toIR.c
index 006c7bc2ff04995192e6245dcedcb36b54cacce3..6175c3bebe95db50910529c9b8f3e341bc16f9ad 100644 (file)
--- a/VEX/priv/guest-x86/toIR.c
+++ b/VEX/priv/guest-x86/toIR.c
@@ -1007,6 +1007,9 @@ void setFlags_DEP1_DEP2 ( IROp op8, IRTemp dep1, IRTemp dep2, IRType ty )
    stmt( IRStmt_Put( OFFB_CC_OP,   mkU32(ccOp)) );
    stmt( IRStmt_Put( OFFB_CC_DEP1, widenUto32(mkexpr(dep1))) );
    stmt( IRStmt_Put( OFFB_CC_DEP2, widenUto32(mkexpr(dep2))) );
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 }
 
 
@@ -1029,6 +1032,9 @@ void setFlags_DEP1 ( IROp op8, IRTemp dep1, IRType ty )
    stmt( IRStmt_Put( OFFB_CC_OP,   mkU32(ccOp)) );
    stmt( IRStmt_Put( OFFB_CC_DEP1, widenUto32(mkexpr(dep1))) );
    stmt( IRStmt_Put( OFFB_CC_DEP2, mkU32(0)) );
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 }
 
 
@@ -1070,6 +1076,9 @@ static void setFlags_DEP1_DEP2_shift ( IROp    op32,
                      IRExpr_Mux0X( mkexpr(guard),
                                    IRExpr_Get(OFFB_CC_DEP2,Ity_I32),
                                    widenUto32(mkexpr(resUS)))) );
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 }
 
 
@@ -1114,6 +1123,9 @@ void setFlags_MUL ( IRType ty, IRTemp arg1, IRTemp arg2, UInt base_op )
    }
    stmt( IRStmt_Put( OFFB_CC_DEP1, widenUto32(mkexpr(arg1)) ));
    stmt( IRStmt_Put( OFFB_CC_DEP2, widenUto32(mkexpr(arg2)) ));
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 }
 
 
@@ -1792,6 +1804,9 @@ void codegen_XOR_reg_with_itself ( Int size, Int ge_reg )
    stmt( IRStmt_Put( OFFB_CC_OP,   mkU32(X86G_CC_OP_COPY) ));
    stmt( IRStmt_Put( OFFB_CC_DEP1, mkU32(X86G_CC_MASK_Z|X86G_CC_MASK_P) ));
    stmt( IRStmt_Put( OFFB_CC_DEP2, mkU32(0) ));
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
    DIP("xor%c %s, %s\n", nameISize(size),
                          nameIReg(size,ge_reg), nameIReg(size,ge_reg) );
 }
@@ -2376,6 +2391,9 @@ UInt dis_Grp2 ( UChar  sorb,
       stmt( IRStmt_Put( OFFB_CC_OP,   mkU32(X86G_CC_OP_COPY) ));
       stmt( IRStmt_Put( OFFB_CC_DEP1, unop(Iop_64HIto32, mkexpr(r64)) ));
       stmt( IRStmt_Put( OFFB_CC_DEP2, mkU32(0) ));
+      /* Set NDEP even though it isn't used.  This makes redundant-PUT
+         elimination of previous stores to this field work better. */
+      stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
    }
 
    if (isShift) {
@@ -2607,6 +2625,9 @@ UInt dis_Grp8_Imm ( UChar       sorb,
                   binop(Iop_Shr32, mkexpr(t2), mkU8(src_val)),
                   mkU32(1))
        ));
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 
    /* Compute the new value into t2m, if non-BT. */
    switch (gregOfRM(modrm)) {
@@ -3574,6 +3595,9 @@ static void fp_do_ucomi_ST0_STi ( UInt i, Bool pop_after )
                             binop(Iop_CmpF64, get_ST(0), get_ST(i)),
                             mkU32(0x45)
        )));
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
    if (pop_after)
       fp_pop();
 }
@@ -5882,6 +5906,9 @@ UInt dis_bt_G_E ( UChar sorb, Int sz, UInt delta, BtOp op )
                         mkexpr(t_bitno2)),
                   mkU32(1)))
        );
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 
    /* Move reg operand from stack back to reg */
    if (epartIsReg(modrm)) {
@@ -5954,6 +5981,9 @@ UInt dis_bs_E_G ( UChar sorb, Int sz, UInt delta, Bool fwds )
                           mkU32(0)
                         )
        ));
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 
    /* Result: iff source value is zero, we can't use
       Iop_Clz32/Iop_Ctz32 as they have no defined result in that case.
@@ -6042,6 +6072,9 @@ void codegen_SAHF ( void )
                      mkU32(mask_SZACP))
               )
    ));
+   /* Set NDEP even though it isn't used.  This makes redundant-PUT
+      elimination of previous stores to this field work better. */
+   stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 }
 
 
@@ -7315,7 +7348,9 @@ DisResult disInstr ( /*IN*/  Bool       resteerOK,
                             unop(Iop_F32toF64,mkexpr(argR))),
                       mkU32(0x45)
           )));
-
+      /* Set NDEP even though it isn't used.  This makes redundant-PUT
+         elimination of previous stores to this field work better. */
+      stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
       goto decode_success;
    }
 
@@ -8324,7 +8359,9 @@ DisResult disInstr ( /*IN*/  Bool       resteerOK,
                       binop(Iop_CmpF64, mkexpr(argL), mkexpr(argR)),
                       mkU32(0x45)
           )));
-
+      /* Set NDEP even though it isn't used.  This makes redundant-PUT
+         elimination of previous stores to this field work better. */
+      stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
       goto decode_success;
    }
 
@@ -11033,6 +11070,9 @@ DisResult disInstr ( /*IN*/  Bool       resteerOK,
                              )
                        )
           );
+      /* Set NDEP even though it isn't used.  This makes redundant-PUT
+         elimination of previous stores to this field work better. */
+      stmt( IRStmt_Put( OFFB_CC_NDEP, mkU32(0) ));
 
       /* Also need to set the D flag, which is held in bit 10 of t1.
          If zero, put 1 in OFFB_DFLAG, else -1 in OFFB_DFLAG. */