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1e8f7ebb6c
It's not pretty, but probably better than modelling it as an opaque SCEVUnknown, i guess. It is relevant e.g. for the loop that was brought up in https://bugs.llvm.org/show_bug.cgi?id=46786#c26 as an example of what we'd be able to better analyze once SCEV handles `ptrtoint` (D89456). But as it is evident, even if we deal with `ptrtoint` there, we also fail to model such an `ashr`. Also, modeling of mul-of-exact-shr/div could use improvement. As per alive2: https://alive2.llvm.org/ce/z/tnfZKd ``` define i8 @src(i8 %0) { %2 = ashr exact i8 %0, 4 ret i8 %2 } declare i8 @llvm.abs(i8, i1) declare i8 @llvm.smin(i8, i8) declare i8 @llvm.smax(i8, i8) define i8 @tgt(i8 %x) { %abs_x = call i8 @llvm.abs(i8 %x, i1 false) %div = udiv exact i8 %abs_x, 16 %t0 = call i8 @llvm.smax(i8 %x, i8 -1) %t1 = call i8 @llvm.smin(i8 %t0, i8 1) %r = mul nsw i8 %div, %t1 ret i8 %r } ``` Transformation seems to be correct!
74 lines
3.0 KiB
LLVM
74 lines
3.0 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
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; RUN: opt < %s --data-layout="e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" -S -analyze -enable-new-pm=0 -scalar-evolution | FileCheck --check-prefixes=ALL,X64 %s
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; RUN: opt < %s --data-layout="e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128" -S -disable-output "-passes=print<scalar-evolution>" 2>&1 | FileCheck --check-prefixes=ALL,X64 %s
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; RUN: opt < %s --data-layout="e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-f64:32:64-f80:32-n8:16:32-S128" -S -analyze -enable-new-pm=0 -scalar-evolution | FileCheck --check-prefixes=ALL,X32 %s
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; RUN: opt < %s --data-layout="e-m:e-p:32:32-p270:32:32-p271:32:32-p272:64:64-f64:32:64-f80:32-n8:16:32-S128" -S -disable-output "-passes=print<scalar-evolution>" 2>&1 | FileCheck --check-prefixes=ALL,X32 %s
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; In general, we can't deal with ashr.
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define i32 @t0(i32 %x, i32 %y) {
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; ALL-LABEL: 't0'
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; ALL-NEXT: Classifying expressions for: @t0
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; ALL-NEXT: %i0 = ashr i32 %x, %y
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; ALL-NEXT: --> %i0 U: full-set S: full-set
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; ALL-NEXT: Determining loop execution counts for: @t0
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;
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%i0 = ashr i32 %x, %y
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ret i32 %i0
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}
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; Not even if we know it's exact
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define i32 @t1(i32 %x, i32 %y) {
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; ALL-LABEL: 't1'
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; ALL-NEXT: Classifying expressions for: @t1
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; ALL-NEXT: %i0 = ashr exact i32 %x, %y
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; ALL-NEXT: --> %i0 U: full-set S: full-set
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; ALL-NEXT: Determining loop execution counts for: @t1
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;
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%i0 = ashr exact i32 %x, %y
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ret i32 %i0
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}
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; Not even if the shift amount is a constant.
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define i32 @t2(i32 %x, i32 %y) {
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; ALL-LABEL: 't2'
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; ALL-NEXT: Classifying expressions for: @t2
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; ALL-NEXT: %i0 = ashr i32 %x, 4
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; ALL-NEXT: --> %i0 U: full-set S: [-134217728,134217728)
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; ALL-NEXT: Determining loop execution counts for: @t2
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;
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%i0 = ashr i32 %x, 4
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ret i32 %i0
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}
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; However, if it's a constant AND the shift is exact, we can model it!
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define i32 @t3(i32 %x, i32 %y) {
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; ALL-LABEL: 't3'
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; ALL-NEXT: Classifying expressions for: @t3
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; ALL-NEXT: %i0 = ashr exact i32 %x, 4
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; ALL-NEXT: --> ((((-1 * %x) smax %x) /u 16) * (1 smin (-1 smax %x)))<nsw> U: [-268435455,268435456) S: [-268435455,268435456)
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; ALL-NEXT: Determining loop execution counts for: @t3
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;
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%i0 = ashr exact i32 %x, 4
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ret i32 %i0
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}
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; As long as the shift amount is in-bounds
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define i32 @t4(i32 %x, i32 %y) {
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; ALL-LABEL: 't4'
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; ALL-NEXT: Classifying expressions for: @t4
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; ALL-NEXT: %i0 = ashr exact i32 %x, 32
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; ALL-NEXT: --> %i0 U: full-set S: full-set
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; ALL-NEXT: Determining loop execution counts for: @t4
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;
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%i0 = ashr exact i32 %x, 32
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ret i32 %i0
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}
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; One more test, just to see that we model constant correctly
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define i32 @t5(i32 %x, i32 %y) {
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; ALL-LABEL: 't5'
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; ALL-NEXT: Classifying expressions for: @t5
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; ALL-NEXT: %i0 = ashr exact i32 %x, 5
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; ALL-NEXT: --> ((((-1 * %x) smax %x) /u 32) * (1 smin (-1 smax %x)))<nsw> U: [-134217727,134217728) S: [-134217727,134217728)
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; ALL-NEXT: Determining loop execution counts for: @t5
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;
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%i0 = ashr exact i32 %x, 5
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ret i32 %i0
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}
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