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| author | Chris Lattner <sabre@nondot.org> | 2011-05-17 07:22:33 +0000 |
|---|---|---|
| committer | Chris Lattner <sabre@nondot.org> | 2011-05-17 07:22:33 +0000 |
| commit | 1e81f57bf0d3f52c990a54b70b5404e240b1fe89 (patch) | |
| tree | 6b564942b7a908dd3557d7597b9f9ce3753a7c51 /llvm/lib | |
| parent | e6a9e439d451fa1741235e157591a7eb7b91a5e7 (diff) | |
| download | bcm5719-llvm-1e81f57bf0d3f52c990a54b70b5404e240b1fe89.tar.gz bcm5719-llvm-1e81f57bf0d3f52c990a54b70b5404e240b1fe89.zip | |
add a note
llvm-svn: 131455
Diffstat (limited to 'llvm/lib')
| -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". + +//===---------------------------------------------------------------------===// + |
