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| author | Jeff Law <jlaw@ventanamicro> | 2023-05-09 07:18:45 -0600 |
|---|---|---|
| committer | Jeff Law <jlaw@ventanamicro> | 2023-05-09 07:18:45 -0600 |
| commit | 204303c81e82ddd01e7dc5a5a63719d476f9043c (patch) | |
| tree | abc87de323cc440f65e603ae73575c61445ada4c /gcc | |
| parent | 2ed5ceba0fe313ef09bdfe98788ba9377bfec9aa (diff) | |
| download | gcc-204303c81e82ddd01e7dc5a5a63719d476f9043c.zip gcc-204303c81e82ddd01e7dc5a5a63719d476f9043c.tar.gz gcc-204303c81e82ddd01e7dc5a5a63719d476f9043c.tar.bz2 | |
Eliminate more comparisons on the H8 port
This patch fixes a minor code quality issue I found while testing LRA on the
H8. Specifically we have a peephole which converts a comparison of a memory
location against zero into a load + comparison which is actually more
efficient. This triggers when there are registers available at the right
point during peephole2.
If the load is not a mode dependent address we can actually do better by
realizing the load itself sets the proper flags and eliminate the comparison.
I may have expected this to happen when I wrote the original peephole2,
but cmpelim runs before peephole2, so clearly if we want to eliminate the
comparison we have to do it manually.
gcc/
* config/h8300/testcompare.md: Add peephole2 which uses a memory
load to set flags, thus eliminating a compare against zero.
Diffstat (limited to 'gcc')
| -rw-r--r-- | gcc/config/h8300/testcompare.md | 14 |
1 files changed, 13 insertions, 1 deletions
diff --git a/gcc/config/h8300/testcompare.md b/gcc/config/h8300/testcompare.md index 81dce1d..efa66d2 100644 --- a/gcc/config/h8300/testcompare.md +++ b/gcc/config/h8300/testcompare.md @@ -171,13 +171,25 @@ (set_attr "length_table" "*,add")]) ;; Convert a memory comparison to a move if there is a scratch register. +;; This is preferred over the next as we can proactively avoid the +;; comparison. +(define_peephole2 + [(match_scratch:QHSI 1 "r") + (set (reg:CC CC_REG) + (compare (match_operand:QHSI 0 "memory_operand" "") + (const_int 0)))] + "!mode_dependent_address_p (XEXP (operands[0], 0), MEM_ADDR_SPACE (operands[0]))" + [(parallel [(set (reg:CCZN CC_REG) (compare:CCZN (match_dup 0) (const_int 0))) + (set (match_dup 1) (match_dup 0))])]) +;; Similarly, but used when the memory reference is an autoinc address +;; mode. (define_peephole2 [(match_scratch:QHSI 1 "r") (set (reg:CC CC_REG) (compare (match_operand:QHSI 0 "memory_operand" "") (const_int 0)))] - "" + "mode_dependent_address_p (XEXP (operands[0], 0), MEM_ADDR_SPACE (operands[0]))" [(parallel [(set (match_dup 1) (match_dup 0)) (clobber (reg:CC CC_REG))]) (set (reg:CC CC_REG) (compare:CC (match_dup 1) (const_int 0)))]) |