diff options
Diffstat (limited to 'lib/Target/README.txt')
| -rw-r--r-- | lib/Target/README.txt | 40 |
1 files changed, 40 insertions, 0 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index ffe3fa477b..0105ae4562 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -2305,4 +2305,44 @@ The two or/and's should be merged into one each. //===---------------------------------------------------------------------===// +Machine level code hoisting can be useful in some cases. For example, PR9408 +is about: + +typedef union { + void (*f1)(int); + void (*f2)(long); +} funcs; + +void foo(funcs f, int which) { + int a = 5; + if (which) { + f.f1(a); + } else { + f.f2(a); + } +} + +which we compile to: + +foo: # @foo +# BB#0: # %entry + pushq %rbp + movq %rsp, %rbp + testl %esi, %esi + movq %rdi, %rax + je .LBB0_2 +# BB#1: # %if.then + movl $5, %edi + callq *%rax + popq %rbp + ret +.LBB0_2: # %if.else + movl $5, %edi + callq *%rax + popq %rbp + ret + +Note that bb1 and bb2 are the same. This doesn't happen at the IR level +because one call is passing an i32 and the other is passing an i64. +//===---------------------------------------------------------------------===// |