diff options
| -rw-r--r-- | lib/Target/README.txt | 35 |
1 files changed, 33 insertions, 2 deletions
diff --git a/lib/Target/README.txt b/lib/Target/README.txt index 06661c9335..655b7a94fe 100644 --- a/lib/Target/README.txt +++ b/lib/Target/README.txt @@ -1716,7 +1716,36 @@ entry: } The srem can be transformed to an and because if x is negative, the shift is -undefined. Testcase derived from gcc. +undefined. Here's a more general case that occurs on 64-bit targets: + + %382 = srem i32 %tmp14.i, 64 ; [#uses=1] + %383 = zext i32 %382 to i64 ; [#uses=1] + %384 = shl i64 %381, %383 ; [#uses=1] + %385 = icmp slt i32 %tmp14.i, 64 ; [#uses=1] + +Testcase derived from 403.gcc. + +//===---------------------------------------------------------------------===// + +This is a range comparison on a divided result (from 403.gcc): + + %1337 = sdiv i32 %1336, 8 ; [#uses=1] + %.off.i208 = add i32 %1336, 7 ; [#uses=1] + %1338 = icmp ult i32 %.off.i208, 15 ; [#uses=1] + +We already catch this (removing the sdiv) if there isn't an add, we should +handle the 'add' as well. This is a common idiom with it's builtin_alloca code. +C testcase: + +int a(int x) { return (unsigned)(x/16+7) < 15; } + +Another similar case involves truncations on 64-bit targets: + + %361 = sdiv i64 %.046, 8 ; [#uses=1] + %362 = trunc i64 %361 to i32 ; [#uses=2] +... + %367 = icmp eq i32 %362, 0 ; [#uses=1] + //===---------------------------------------------------------------------===// @@ -1729,7 +1758,9 @@ entry: } Should compile to something like x+y*8, but currently compiles to an -inefficient result. Testcase derived from gcc. +inefficient result. Testcase derived from gcc. C testcase: + +int a(int x, int y) { return y-x*-8; } //===---------------------------------------------------------------------===// |