llvm-mirror/test/Transforms/InstSimplify/exact-nsw-nuw.ll
Sanjay Patel 3e2b1fd515 [InstSimplify] fold sdiv/srem based on compare of dividend and divisor
This should bring signed div/rem analysis up to the same level as unsigned. 
We use icmp simplification to determine when the divisor is known greater than the dividend.

Each positive test is followed by a negative test to show that we're not overstepping the boundaries of the known bits.
There are extra tests for the signed-min-value special cases.

Alive proofs:
http://rise4fun.com/Alive/WI5

Differential Revision: https://reviews.llvm.org/D37713

llvm-svn: 313264
2017-09-14 14:59:07 +00:00

70 lines
1.2 KiB
LLVM

; RUN: opt < %s -instsimplify -S | FileCheck %s
; PR8862
define i32 @shift1(i32 %A, i32 %B) {
; CHECK-LABEL: @shift1(
; CHECK-NEXT: ret i32 %A
;
%C = lshr exact i32 %A, %B
%D = shl nuw i32 %C, %B
ret i32 %D
}
define i32 @shift2(i32 %A, i32 %B) {
; CHECK-LABEL: @shift2(
; CHECK-NEXT: [[C:%.*]] = lshr i32 %A, %B
; CHECK-NEXT: [[D:%.*]] = shl nuw i32 [[C]], %B
; CHECK-NEXT: ret i32 [[D]]
;
%C = lshr i32 %A, %B
%D = shl nuw i32 %C, %B
ret i32 %D
}
define i32 @shift3(i32 %A, i32 %B) {
; CHECK-LABEL: @shift3(
; CHECK-NEXT: ret i32 %A
;
%C = ashr exact i32 %A, %B
%D = shl nuw i32 %C, %B
ret i32 %D
}
define i32 @shift4(i32 %A, i32 %B) {
; CHECK-LABEL: @shift4(
; CHECK-NEXT: ret i32 %A
;
%C = shl nuw i32 %A, %B
%D = lshr i32 %C, %B
ret i32 %D
}
define i32 @shift5(i32 %A, i32 %B) {
; CHECK-LABEL: @shift5(
; CHECK-NEXT: ret i32 %A
;
%C = shl nsw i32 %A, %B
%D = ashr i32 %C, %B
ret i32 %D
}
define i32 @div1(i32 %V) {
; CHECK-LABEL: @div1(
; CHECK-NEXT: ret i32 0
;
%A = udiv i32 %V, -2147483648
%B = udiv i32 %A, -2147483648
ret i32 %B
}
define i32 @div2(i32 %V) {
; CHECK-LABEL: @div2(
; CHECK-NEXT: ret i32 0
;
%A = sdiv i32 %V, -1
%B = sdiv i32 %A, -2147483648
ret i32 %B
}