[llvm] 5b96b13 - [SCEV] Improve AddRecs' range computation in Expensive Range Sharpening mode

[Max Kazantsev via llvm-commits]

Author: Max Kazantsev
Date: 2023-04-10T16:37:10+07:00
New Revision: 5b96b13fdffebc1e81cdca3466e75b0d0e584c27

URL: https://github.com/llvm/llvm-project/commit/5b96b13fdffebc1e81cdca3466e75b0d0e584c27
DIFF: https://github.com/llvm/llvm-project/commit/5b96b13fdffebc1e81cdca3466e75b0d0e584c27.diff

LOG: [SCEV] Improve AddRecs' range computation in Expensive Range Sharpening mode

Apply loop guards to AddRec's start in range computation for
non-self-wrapping AddRecs.

According to CT measurements, this has a wide negative compile time impact,
so we hold it in expensive range sharpening mode where it's not so critical.
However, we need to find a way to share benefits of this mode with default mode.

Patch by Aleksandr Popov!

Differential Revision: https://reviews.llvm.org/D147557
Reviewed By: mkazantsev

Added: 
    

Modified: 
    llvm/lib/Analysis/ScalarEvolution.cpp
    llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll

Removed: 
    


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diff  --git a/llvm/lib/Analysis/ScalarEvolution.cpp b/llvm/lib/Analysis/ScalarEvolution.cpp
index a2f0aa4e96cd7..174eea8d364ab 100644
--- a/llvm/lib/Analysis/ScalarEvolution.cpp
+++ b/llvm/lib/Analysis/ScalarEvolution.cpp
@@ -7003,7 +7003,7 @@ ConstantRange ScalarEvolution::getRangeForAffineNoSelfWrappingAR(
   // outside and inside the range [Min(Start, End), Max(Start, End)]. Using that
   // knowledge, let's try to prove that we are dealing with Case 1. It is so if
   // Start <= End and step is positive, or Start >= End and step is negative.
-  const SCEV *Start = AddRec->getStart();
+  const SCEV *Start = applyLoopGuards(AddRec->getStart(), AddRec->getLoop());
   ConstantRange StartRange = getRangeRef(Start, SignHint);
   ConstantRange EndRange = getRangeRef(End, SignHint);
   ConstantRange RangeBetween = StartRange.unionWith(EndRange);

diff  --git a/llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll b/llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
index e4453328f37a8..3757ffc693a9a 100644
--- a/llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
+++ b/llvm/test/Analysis/ScalarEvolution/decrementing_addrecs.ll
@@ -23,8 +23,8 @@
 ; FIXME: c's AddRec is expected to be no-sign-wrap
 ;        i is expected to be non-negative
 ;        j is expected to be non-negative
-; FIXME: a is expected to be positive
-; FIXME: b is expected to be non-negative
+;        a is expected to be positive
+;        b is expected to be non-negative
 ;        c is expected to be positive
 define i32 @test_step_1_flags(i32 %n) {
 ; DEFAULT-LABEL: 'test_step_1_flags'
@@ -60,17 +60,17 @@ define i32 @test_step_1_flags(i32 %n) {
 ; EXPENSIVE_SHARPENING-NEXT:    %i = phi i32 [ 0, %entry ], [ %i.next, %loop ]
 ; EXPENSIVE_SHARPENING-NEXT:    --> {0,+,1}<nuw><nsw><%loop> U: [0,2147483647) S: [0,2147483647) Exits: (-1 + %n) LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %j = phi i32 [ %n.minus.1, %entry ], [ %j.next, %loop ]
-; EXPENSIVE_SHARPENING-NEXT:    --> {(-1 + %n),+,-1}<nsw><%loop> U: full-set S: full-set Exits: 0 LoopDispositions: { %loop: Computable }
+; EXPENSIVE_SHARPENING-NEXT:    --> {(-1 + %n),+,-1}<nsw><%loop> U: [0,2147483647) S: [0,2147483647) Exits: 0 LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %a = sub i32 %n, %i
-; EXPENSIVE_SHARPENING-NEXT:    --> {%n,+,-1}<nw><%loop> U: full-set S: full-set Exits: 1 LoopDispositions: { %loop: Computable }
+; EXPENSIVE_SHARPENING-NEXT:    --> {%n,+,-1}<nw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: 1 LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %b = sub i32 %n.minus.1, %i
-; EXPENSIVE_SHARPENING-NEXT:    --> {(-1 + %n),+,-1}<nsw><%loop> U: full-set S: full-set Exits: 0 LoopDispositions: { %loop: Computable }
+; EXPENSIVE_SHARPENING-NEXT:    --> {(-1 + %n),+,-1}<nsw><%loop> U: [0,2147483647) S: [0,2147483647) Exits: 0 LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %c = sub i32 2147483647, %i
 ; EXPENSIVE_SHARPENING-NEXT:    --> {2147483647,+,-1}<nw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: (-2147483648 + (-1 * %n)) LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %i.next = add nuw nsw i32 %i, 1
 ; EXPENSIVE_SHARPENING-NEXT:    --> {1,+,1}<nuw><nsw><%loop> U: [1,-2147483648) S: [1,-2147483648) Exits: %n LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:    %j.next = add nsw i32 %j, -1
-; EXPENSIVE_SHARPENING-NEXT:    --> {(-2 + %n),+,-1}<nw><%loop> U: full-set S: full-set Exits: -1 LoopDispositions: { %loop: Computable }
+; EXPENSIVE_SHARPENING-NEXT:    --> {(-2 + %n),+,-1}<nsw><%loop> U: full-set S: [-1,2147483646) Exits: -1 LoopDispositions: { %loop: Computable }
 ; EXPENSIVE_SHARPENING-NEXT:  Determining loop execution counts for: @test_step_1_flags
 ; EXPENSIVE_SHARPENING-NEXT:  Loop %loop: backedge-taken count is (-1 + %n)
 ; EXPENSIVE_SHARPENING-NEXT:  Loop %loop: constant max backedge-taken count is 2147483646