[PATCH] Add field to InstAlias used to instruct AsmMatcherEmitter to ignore alias

[Jim Grosbach]

This should be solved differently. InstAliases are for the parser and should never be ignored, so ambiguous aliases is an indication of a bigger problem.

-Jim


On Jul 19, 2013, at 12:51 PM, Akira Hatanaka <ahatanak at gmail.com> wrote:

> The attached patch (instalias1.patch) adds field "Assemble", which AsmMatcherEmitter can use to decide whether it should ignore the alias.
> 
> This is needed when there are two InstAlias patterns with the same AsmString. For example, in MipsInstrInfo.td, there are two patterns which have the .s format, "move $dst, $src":
> 
> def : InstAlias<"move $dst, $src",
>                 (ADDu CPURegsOpnd:$dst, CPURegsOpnd:$src,ZERO), 1>,
>       Requires<[NotMips64]>;
> def : InstAlias<"move $dst, $src",
>                 (OR CPURegsOpnd:$dst, CPURegsOpnd:$src,ZERO), 1>,
> 
> We need two aliases here because we want to have instPrinter print a "move" instruction instead of an "addu" or "or" when one of the operands is $zero:
> 
> "addu $2, $3, $zero" or "or $2, $3, $zero" =>  "move $2, $3"
> 
> However, this causes tablegen to place two entries in array MatchTable in MipsGenAsmMatcher.inc:
> 
>   { 1364 /* move */, Mips::OR, Convert__CPURegsAsm1_0__CPURegsAsm1_1__regZERO, Feature_NotMips64, { MCK_CPURegsAsm, MCK_CPURegsAsm }, 0},
>   { 1364 /* move */, Mips::ADDu, Convert__CPURegsAsm1_0__CPURegsAsm1_1__regZERO, Feature_NotMips64, { MCK_CPURegsAsm, MCK_CPURegsAsm }, 0},
> 
> The order in which these entries appear in the table seems arbitrary, as I discovered when  I made completely unrelated changes in other places. We want to have the assembler generate an "ADDu" instruction and ignore the pattern with "OR". 
> 
> Please review.
> 
> <instalias1.patch><instalias-mips.patch>_______________________________________________
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