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| -rw-r--r-- | lib/Target/README.txt | 28 |
1 files changed, 28 insertions, 0 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index b27d99e18b..d1e4bfb075 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1984,3 +1984,31 @@ void check_c28 () { } //===---------------------------------------------------------------------===// + +We compile this: + +int foo(int a) { return (a & (~15)) / 16; } + +Into: + +define i32 @foo(i32 %a) nounwind readnone ssp { +entry: + %and = and i32 %a, -16 + %div = sdiv i32 %and, 16 + ret i32 %div +} + +but this code (X & -A)/A is X >> log2(A) when A is a power of 2, so this case +should be instcombined into just "a >> 4". + +We do get this at the codegen level, so something knows about it, but +instcombine should catch it earlier: + +_foo: ## @foo +## BB#0: ## %entry + movl %edi, %eax + sarl $4, %eax + ret + +//===---------------------------------------------------------------------===// + |