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6712e20c52
Added Support for flag output operand "=@cc", inline assembly constraint
for
SystemZ.
- Clang now accepts "=@cc" assembly operands, and sets 2-bits condition
code
for output operand for SyatemZ.
- Clang currently emits an assertion that flag output operands are
boolean
values, i.e. in the range [0, 2). Generalize this mechanism to allow
targets to specify arbitrary range assertions for any inline assembly
output operand. This will be used to assert that SystemZ two-bit
condition-code values are in the range [0, 4).
- SystemZ backend lowers "@cc" targets by using ipm sequence to extract
condition code from PSW.
- DAGCombine tries to optimize lowered ipm sequence by combining
CCReg and computing effective CCMask and CCValid in combineCCMask for
select_ccmask and br_ccmask.
- Cost computation is done for merging conditionals for branch
instruction
in SelectionDAG, as split may cause branches conditions evaluation goes
across basic block and difficult to combine.
---------
Co-authored-by: anoopkg6 <anoopkg6@github.com>
Co-authored-by: Ulrich Weigand <ulrich.weigand@de.ibm.com>
IRgen optimization opportunities. //===---------------------------------------------------------------------===// The common pattern of -- short x; // or char, etc (x == 10) -- generates an zext/sext of x which can easily be avoided. //===---------------------------------------------------------------------===// Bitfields accesses can be shifted to simplify masking and sign extension. For example, if the bitfield width is 8 and it is appropriately aligned then is is a lot shorter to just load the char directly. //===---------------------------------------------------------------------===// It may be worth avoiding creation of alloca's for formal arguments for the common situation where the argument is never written to or has its address taken. The idea would be to begin generating code by using the argument directly and if its address is taken or it is stored to then generate the alloca and patch up the existing code. In theory, the same optimization could be a win for block local variables as long as the declaration dominates all statements in the block. NOTE: The main case we care about this for is for -O0 -g compile time performance, and in that scenario we will need to emit the alloca anyway currently to emit proper debug info. So this is blocked by being able to emit debug information which refers to an LLVM temporary, not an alloca. //===---------------------------------------------------------------------===// We should try and avoid generating basic blocks which only contain jumps. At -O0, this penalizes us all the way from IRgen (malloc & instruction overhead), all the way down through code generation and assembly time. On 176.gcc:expr.ll, it looks like over 12% of basic blocks are just direct branches! //===---------------------------------------------------------------------===//