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git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@119925 91177308-0d34-0410-b5e6-96231b3b80d8
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Chris Lattner 2010-11-21 07:05:31 +00:00
parent aa54524a44
commit 3e41106de4
1 changed files with 33 additions and 2 deletions
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35
lib/Target/README.txt
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@ -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; }
//===---------------------------------------------------------------------===//