llvm/test/Transforms/InstCombine/preserve-sminmax.ll
Dan Gohman 81b28ceab6 Improve instcombine's handling of integer min and max in two ways:
- Recognize expressions like "x > -1 ? x : 0" as min/max and turn them
   into expressions like "x < 0 ? 0 : x", which is easily recognizable
   as a min/max operation.
 - Refrain from folding expression like "y/2 < 1" to "y < 2" when the
   comparison is being used as part of a min or max idiom, like
   "y/2 < 1 ? 1 : y/2". In that case, the division has another use, so
   folding doesn't eliminate it, and obfuscates the min/max, making it
   harder to recognize as a min/max operation.

These benefit ScalarEvolution, CodeGen, and anything else that wants to
recognize integer min and max.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@56246 91177308-0d34-0410-b5e6-96231b3b80d8
2008-09-16 18:46:06 +00:00

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654 B
LLVM

; RUN: llvm-as < %s | opt -instcombine | llvm-dis | grep { i32 \[%\]sd, \[\[:alnum:\]\]* \\?1\\>} | count 4
; Instcombine normally would fold the sdiv into the comparison,
; making "icmp slt i32 %h, 2", but in this case the sdiv has
; another use, so it wouldn't a big win, and it would also
; obfuscate an otherise obvious smax pattern to the point where
; other analyses wouldn't recognize it.
define i32 @foo(i32 %h) {
%sd = sdiv i32 %h, 2
%t = icmp slt i32 %sd, 1
%r = select i1 %t, i32 %sd, i32 1
ret i32 %r
}
define i32 @bar(i32 %h) {
%sd = sdiv i32 %h, 2
%t = icmp sgt i32 %sd, 1
%r = select i1 %t, i32 %sd, i32 1
ret i32 %r
}