Enhance MemDep: When alias analysis returns a partial alias result,
return it as a clobber. This allows GVN to do smart things. Enhance GVN to be smart about the case when a small load is clobbered by a larger overlapping load. In this case, forward the value. This allows us to compile stuff like this: int test(void *P) { int tmp = *(unsigned int*)P; return tmp+*((unsigned char*)P+1); } into: _test: ## @test movl (%rdi), %ecx movzbl %ch, %eax addl %ecx, %eax ret which has one load. We already handled the case where the smaller load was from a must-aliased base pointer. llvm-svn: 130180
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