9a7286b61f
Recent improvements in symbolic exit count computation revealed some problems with SCEV's ability to find invariant predicate during first iterations. Ultimately it is based on its ability to prove some facts for value on the last iteration. This last value, when it includes `umin` as part of exit count, isn't always simplified enough. The motivating example is following: https://github.com/llvm/llvm-project/issues/59615 Could not prove: ``` Pred = 36, LHS = (-1 + (-1 * (2147483645 umin (-1 + %var)<nsw>))<nsw> + %var), RHS = %var FoundPred = 36, FoundLHS = {1,+,1}<nuw><nsw><%bb3>, FoundRHS = %var ``` Can prove: ``` Pred = 36, LHS = (-1 + (-1 * (-1 + %var)<nsw>)<nsw> + %var), RHS = %var FoundPred = 36, FoundLHS = {1,+,1}<nuw><nsw><%bb3>, FoundRHS = %var ``` Here ` (2147483645 umin (-1 + %var)<nsw>)` is exit count composed of two parts from two different exits: `2147483645 ` and `(-1 + %var)<nsw>`. When it was only one (latter) analyzeable exit, for it everything was easily provable. Unfortunately, in general case `umin` in one of `add`'s operands doesn't guarantee that the whole sum reduces, especially in presence of negative steps and lack of `nuw`. I don't think there is a generic legal way to somehow play around this `umin`. So the ad-hoc solution is following: if we failed to find an equivalent predicate that is invariant during first `MaxIter` iterations, and `MaxIter = umin(a, b, c...)`, try to find solution for at least one of `a`, `b`, `c`... Because they all are `uge` than `MaxIter`, whatever is true during `a (b, c)` iterations is also true during `MaxIter` iterations. Differential Revision: https://reviews.llvm.org/D140456 Reviewed By: nikic
79 lines
3.1 KiB
LLVM
79 lines
3.1 KiB
LLVM
; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
|
|
; RUN: opt -passes='loop(indvars),verify' -S < %s | FileCheck %s
|
|
|
|
target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-f80:128-n8:16:32:64-S128-ni:1-p2:32:8:8:32-ni:2"
|
|
target triple = "x86_64-unknown-linux-gnu"
|
|
|
|
define void @test() {
|
|
; CHECK-LABEL: @test(
|
|
; CHECK-NEXT: bb:
|
|
; CHECK-NEXT: [[VAR:%.*]] = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range [[RNG0:![0-9]+]], !invariant.load !1, !noundef !1
|
|
; CHECK-NEXT: [[VAR2:%.*]] = icmp eq i32 [[VAR]], 0
|
|
; CHECK-NEXT: br i1 [[VAR2]], label [[BB18:%.*]], label [[BB19:%.*]]
|
|
; CHECK: bb3:
|
|
; CHECK-NEXT: [[INDVARS_IV:%.*]] = phi i64 [ 0, [[BB19]] ], [ [[INDVARS_IV_NEXT:%.*]], [[BB12:%.*]] ]
|
|
; CHECK-NEXT: br i1 true, label [[BB8:%.*]], label [[BB7:%.*]]
|
|
; CHECK: bb7:
|
|
; CHECK-NEXT: ret void
|
|
; CHECK: bb8:
|
|
; CHECK-NEXT: [[VAR9:%.*]] = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range [[RNG0]], !invariant.load !1, !noundef !1
|
|
; CHECK-NEXT: [[TMP0:%.*]] = zext i32 [[VAR9]] to i64
|
|
; CHECK-NEXT: [[VAR10:%.*]] = icmp ult i64 [[INDVARS_IV]], [[TMP0]]
|
|
; CHECK-NEXT: br i1 [[VAR10]], label [[BB12]], label [[BB11:%.*]]
|
|
; CHECK: bb11:
|
|
; CHECK-NEXT: ret void
|
|
; CHECK: bb12:
|
|
; CHECK-NEXT: [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
|
|
; CHECK-NEXT: [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[TMP1:%.*]]
|
|
; CHECK-NEXT: br i1 [[EXITCOND]], label [[BB3:%.*]], label [[BB17:%.*]]
|
|
; CHECK: bb17:
|
|
; CHECK-NEXT: unreachable
|
|
; CHECK: bb18:
|
|
; CHECK-NEXT: ret void
|
|
; CHECK: bb19:
|
|
; CHECK-NEXT: [[TMP1]] = zext i32 [[VAR]] to i64
|
|
; CHECK-NEXT: br label [[BB3]]
|
|
;
|
|
bb:
|
|
%var = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range !0, !invariant.load !1, !noundef !1
|
|
%var1 = add nsw i32 %var, -1
|
|
%var2 = icmp eq i32 %var, 0
|
|
br i1 %var2, label %bb18, label %bb19
|
|
|
|
bb3: ; preds = %bb19, %bb12
|
|
%var4 = phi i32 [ %var15, %bb12 ], [ 0, %bb19 ]
|
|
%var5 = sub nsw i32 %var1, %var4
|
|
%var6 = icmp ult i32 %var5, %var
|
|
br i1 %var6, label %bb8, label %bb7
|
|
|
|
bb7: ; preds = %bb3
|
|
ret void
|
|
|
|
bb8: ; preds = %bb3
|
|
%var9 = load atomic i32, ptr addrspace(1) poison unordered, align 8, !range !0, !invariant.load !1, !noundef !1
|
|
%var10 = icmp ult i32 %var4, %var9
|
|
br i1 %var10, label %bb12, label %bb11
|
|
|
|
bb11: ; preds = %bb8
|
|
ret void
|
|
|
|
bb12: ; preds = %bb8
|
|
%var13 = zext i32 %var4 to i64
|
|
%var14 = getelementptr inbounds i32, ptr addrspace(1) poison, i64 %var13
|
|
%var15 = add nuw nsw i32 %var4, 1
|
|
%var16 = icmp ult i32 %var15, %var
|
|
br i1 %var16, label %bb3, label %bb17
|
|
|
|
bb17: ; preds = %bb12
|
|
unreachable
|
|
|
|
bb18: ; preds = %bb
|
|
ret void
|
|
|
|
bb19: ; preds = %bb
|
|
br label %bb3
|
|
}
|
|
|
|
!0 = !{i32 0, i32 2147483646}
|
|
!1 = !{}
|