Lower the i8 extension in memset to a multiply instead of a potentially long...
Lower the i8 extension in memset to a multiply instead of a potentially long series of shifts and ors. We could implement a DAGCombine to turn x * 0x0101 back into logic operations on targets that doesn't support the multiply or it is slow (p4) if someone cares enough. Example code: void test(char *s, int a) { __builtin_memset(s, a, 4); } before: _test: ## @test movzbl 8(%esp), %eax movl %eax, %ecx shll $8, %ecx orl %eax, %ecx movl %ecx, %eax shll $16, %eax orl %ecx, %eax movl 4(%esp), %ecx movl %eax, 4(%ecx) movl %eax, (%ecx) ret after: _test: ## @test movzbl 8(%esp), %eax imull $16843009, %eax, %eax ## imm = 0x1010101 movl 4(%esp), %ecx movl %eax, 4(%ecx) movl %eax, (%ecx) ret llvm-svn: 122707
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