%AConst = constant int 123 implementation ; A SetCC whose result is used should produce instructions to ; compute the boolean value in a register. One whose result ; is unused will only generate the condition code but not ; the boolean result. ; void "unusedBool"(int * %x, int * %y) begin ; <label>:0 ; [#uses=0] seteq int * %x, %y ; <bool>:0 [#uses=1] not bool %0 ; <bool>:1 [#uses=0] setne int * %x, %y ; <bool>:2 [#uses=0] ret void end ; A constant argument to a Phi produces a Cast instruction in the ; corresponding predecessor basic block. This checks a few things: ; -- phi arguments coming from the bottom of the same basic block ; (they should not be forward substituted in the machine code!) ; -- code generation for casts of various types ; -- use of immediate fields for integral constants of different sizes ; -- branch on a constant condition ; void "mergeConstants"(int * %x, int * %y) begin ; <label>:0 br label %Top Top: phi int [ 0, %0 ], [ 1, %Top ], [ 524288, %Next ] phi float [ 0.0, %0 ], [ 1.0, %Top ], [ 2.0, %Next ] phi double [ 0.5, %0 ], [ 1.5, %Top ], [ 2.5, %Next ] phi bool [ true, %0 ], [ false,%Top ], [ true, %Next ] br bool true, label %Top, label %Next Next: br label %Top end ; A constant argument to a cast used only once should be forward substituted ; and loaded where needed, which happens is: ; -- User of cast has no immediate field ; -- User of cast has immediate field but constant is too large to fit ; or constant is not resolved until later (e.g., global address) ; -- User of cast uses it as a call arg. or return value so it is an implicit ; use but has to be loaded into a virtual register so that the reg. ; allocator can allocate the appropriate phys. reg. for it ; int* "castconst"(float) begin ; <label>:0 %castbig = cast ulong 99999999 to int %castsmall = cast ulong 1 to int %usebig = add int %castbig, %castsmall %castglob = cast int* %AConst to long* %dummyl = load long* %castglob %castnull = cast ulong 0 to int* ret int* %castnull end ; Test branch-on-comparison-with-zero, in two ways: ; 1. can be folded ; 2. cannot be folded because result of comparison is used twice ; void "testbool"(int, int) ; Def %0, %1 const int 0 ; Def 2 const int -4 ; Def 3 begin ; <label>:0 br label %Top Top: add int %0, %1 ; Def 4 sub int %4, %3 ; Def 5 setle int %5, %2 ; Def 0 - bool plane br bool %0, label %retlbl, label %loop loop: add int %0, %1 ; Def 6 sub int %4, %3 ; Def 7 setle int %7, %2 ; Def 1 - bool not bool %1 ; Def 2 - bool. first use of bool %1 br bool %1, label %loop, label %Top ; second use of bool %1 retlbl: ret void end ; Test branch on floating point comparison ; void "testfloatbool"(float %x, float %y) ; Def %0, %1 - float begin ; <label>:0 br label %Top Top: %p = add float %x, %y ; Def 2 - float %z = sub float %x, %y ; Def 3 - float %b = setle float %p, %z ; Def 0 - bool %c = not bool %b ; Def 1 - bool br bool %b, label %Top, label %goon goon: ret void end ; Test cases where an LLVM instruction requires no machine ; instructions (e.g., cast int* to long). But there are 2 cases: ; 1. If the result register has only a single use and the use is in the ; same basic block, the operand will be copy-propagated during ; instruction selection. ; 2. If the result register has multiple uses or is in a different ; basic block, it cannot (or will not) be copy propagated during ; instruction selection. It will generate a ; copy instruction (add-with-0), but this copy should get coalesced ; away by the register allocator. ; int "checkForward"(int %N, int* %A) begin bb2: ;;<label> %reg114 = shl int %N, ubyte 2 ;; %cast115 = cast int %reg114 to int* ;; reg114 will be propagated %reg116 = add int* %A, %cast115 ;; %reg118 = load int* %reg116 ;; %cast117 = cast int %reg118 to long ;; reg118 will be copied 'cos %reg159 = add long 1234567, %cast117 ;; cast117 has 2 uses, here %reg160 = add long 7654321, %cast117 ;; and here. ret void end