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author | Chris Lattner <sabre@nondot.org> | 2010-12-26 03:53:31 +0000 |
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committer | Chris Lattner <sabre@nondot.org> | 2010-12-26 03:53:31 +0000 |
commit | 8a4893e01380d63938b86bd8934ea19b5e8008f1 (patch) | |
tree | a6620ff167e2287d2cfed4210a9d51c4182acdf6 /lib/Target/X86/README.txt | |
parent | 7ab3cc32d6bd3c3166184e27713c91f5317c7f85 (diff) | |
download | external_llvm-8a4893e01380d63938b86bd8934ea19b5e8008f1.zip external_llvm-8a4893e01380d63938b86bd8934ea19b5e8008f1.tar.gz external_llvm-8a4893e01380d63938b86bd8934ea19b5e8008f1.tar.bz2 |
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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@122559 91177308-0d34-0410-b5e6-96231b3b80d8
Diffstat (limited to 'lib/Target/X86/README.txt')
-rw-r--r-- | lib/Target/X86/README.txt | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index d199a37..6b83d47 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -96,6 +96,97 @@ It appears icc use push for parameter passing. Need to investigate. //===---------------------------------------------------------------------===// +This: + +void foo(void); +void bar(int x, int *P) { + x >>= 2; + if (x) + foo(); + *P = x; +} + +compiles into: + + movq %rsi, %rbx + movl %edi, %r14d + sarl $2, %r14d + testl %r14d, %r14d + je LBB0_2 + +Instead of doing an explicit test, we can use the flags off the sar. This +occurs in a bigger testcase like this, which is pretty common: + +#include <vector> + + +int test1(std::vector<int> &X) { + int Sum = 0; + for (long i = 0, e = X.size(); i != e; ++i) + X[i] = 0; + return Sum; +} +compiles into: + + movq %rsi, %rbx + movl %edi, %r14d + sarl $2, %r14d + testl %r14d, %r14d + je LBB0_2 + +Instead of doing an explicit test, we can use the flags off the sar. This +occurs in a bigger testcase like this, which is pretty common: + +#include <vector> + + +int test1(std::vector<int> &X) { + int Sum = 0; + for (long i = 0, e = X.size(); i != e; ++i) + X[i] = 0; + return Sum; +} +compiles into: + + movq %rsi, %rbx + movl %edi, %r14d + sarl $2, %r14d + testl %r14d, %r14d + je LBB0_2 + +Instead of doing an explicit test, we can use the flags off the sar. This +occurs in a bigger testcase like this, which is pretty common: + +#include <vector> + + +int test1(std::vector<int> &X) { + int Sum = 0; + for (long i = 0, e = X.size(); i != e; ++i) + X[i] = 0; + return Sum; +} +compiles into: + + movq %rsi, %rbx + movl %edi, %r14d + sarl $2, %r14d + testl %r14d, %r14d + je LBB0_2 + +Instead of doing an explicit test, we can use the flags off the sar. This +occurs in a bigger testcase like this, which is pretty common in bootstrap: + +#include <vector> +int test1(std::vector<int> &X) { + int Sum = 0; + for (long i = 0, e = X.size(); i != e; ++i) + X[i] = 0; + return Sum; +} + +//===---------------------------------------------------------------------===// + Only use inc/neg/not instructions on processors where they are faster than add/sub/xor. They are slower on the P4 due to only updating some processor flags. |