diff options
| -rw-r--r-- | lib/Target/X86/README.txt | 41 |
1 files changed, 41 insertions, 0 deletions
diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt index 9a380acc6b..e8c2561d41 100644 --- a/lib/Target/X86/README.txt +++ b/lib/Target/X86/README.txt @@ -1777,3 +1777,44 @@ LBB1_2: ## overflow it would be nice to produce "into" someday. //===---------------------------------------------------------------------===// + +This code: + +void vec_mpys1(int y[], const int x[], int scaler) { +int i; +for (i = 0; i < 150; i++) + y[i] += (((long long)scaler * (long long)x[i]) >> 31); +} + +Compiles to this loop with GCC 3.x: + +.L5: + movl %ebx, %eax + imull (%edi,%ecx,4) + shrdl $31, %edx, %eax + addl %eax, (%esi,%ecx,4) + incl %ecx + cmpl $149, %ecx + jle .L5 + +llvm-gcc compiles it to the much uglier: + +LBB1_1: ## bb1 + movl 24(%esp), %eax + movl (%eax,%edi,4), %ebx + movl %ebx, %ebp + imull %esi, %ebp + movl %ebx, %eax + mull %ecx + addl %ebp, %edx + sarl $31, %ebx + imull %ecx, %ebx + addl %edx, %ebx + shldl $1, %eax, %ebx + movl 20(%esp), %eax + addl %ebx, (%eax,%edi,4) + incl %edi + cmpl $150, %edi + jne LBB1_1 ## bb1 + +//===---------------------------------------------------------------------===// |