diff options
Diffstat (limited to 'llvm/lib/Target/X86')
| -rw-r--r-- | llvm/lib/Target/X86/README.txt | 26 |
1 files changed, 26 insertions, 0 deletions
diff --git a/llvm/lib/Target/X86/README.txt b/llvm/lib/Target/X86/README.txt index ea3014e7b92..560947a4a04 100644 --- a/llvm/lib/Target/X86/README.txt +++ b/llvm/lib/Target/X86/README.txt @@ -2040,3 +2040,29 @@ _clamp2: ## @clamp2 The move of 0 could be scheduled above the test to make it is xor reg,reg. //===---------------------------------------------------------------------===// + +GCC PR48986. We currently compile this: + +void bar(void); +void yyy(int* p) { + if (__sync_fetch_and_add(p, -1) == 1) + bar(); +} + +into: + movl $-1, %eax + lock + xaddl %eax, (%rdi) + cmpl $1, %eax + je LBB0_2 + +Instead we could generate: + + lock + dec %rdi + je LBB0_2 + +The trick is to match "fetch_and_add(X, -C) == C". + +//===---------------------------------------------------------------------===// + |
