[llvm] r374835 - [Tests] Add a SCEV analysis test for llvm.widenable.condition

[Philip Reames via llvm-commits]

Author: reames
Date: Mon Oct 14 15:42:35 2019
New Revision: 374835

URL: http://llvm.org/viewvc/llvm-project?rev=374835&view=rev
Log:
[Tests] Add a SCEV analysis test for llvm.widenable.condition

Mostly because we don't appear to have one and a prototype patch I just saw would have broken the example committed.


Added:
    llvm/trunk/test/Analysis/ScalarEvolution/widenable-condition.ll

Added: llvm/trunk/test/Analysis/ScalarEvolution/widenable-condition.ll
URL: http://llvm.org/viewvc/llvm-project/llvm/trunk/test/Analysis/ScalarEvolution/widenable-condition.ll?rev=374835&view=auto
==============================================================================
--- llvm/trunk/test/Analysis/ScalarEvolution/widenable-condition.ll (added)
+++ llvm/trunk/test/Analysis/ScalarEvolution/widenable-condition.ll Mon Oct 14 15:42:35 2019
@@ -0,0 +1,45 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt -analyze -scalar-evolution < %s | FileCheck %s
+
+; The semanics of this example are a bit subtle.  The loop is required
+; execute some number of times up to 1999.  The compiler is free to reduce
+; the number of said iterations to zero (or any value in between) if desired,
+; but if it does so, the return value and the last value stored to G must
+; agree.  For SCEV, this translates as widenable conditions preventing exact
+; exit counts from being computed, but not restricting max exit counts.
+; It's tempting to say that SCEV should return a precise exit count here, but
+; would result in miscompiles if transformations such as RLEV ran before
+; widening of the WC.
+define i32 @wc_max() {
+; CHECK-LABEL: 'wc_max'
+; CHECK-NEXT:  Classifying expressions for: @wc_max
+; CHECK-NEXT:    %iv = phi i32 [ 0, %entry ], [ %iv.next, %loop ]
+; CHECK-NEXT:    --> {0,+,1}<%loop> U: [0,2000) S: [0,2000) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    %iv.next = add i32 %iv, 1
+; CHECK-NEXT:    --> {1,+,1}<%loop> U: [1,2001) S: [1,2001) Exits: <<Unknown>> LoopDispositions: { %loop: Computable }
+; CHECK-NEXT:    %widenable_cond3 = call i1 @llvm.experimental.widenable.condition()
+; CHECK-NEXT:    --> %widenable_cond3 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT:    %exiplicit_guard_cond4 = and i1 %cond_1, %widenable_cond3
+; CHECK-NEXT:    --> %exiplicit_guard_cond4 U: full-set S: full-set Exits: <<Unknown>> LoopDispositions: { %loop: Variant }
+; CHECK-NEXT:  Determining loop execution counts for: @wc_max
+; CHECK-NEXT:  Loop %loop: Unpredictable backedge-taken count.
+; CHECK-NEXT:  Loop %loop: max backedge-taken count is 1999
+; CHECK-NEXT:  Loop %loop: Unpredictable predicated backedge-taken count.
+;
+entry:
+  br label %loop
+loop:
+  %iv = phi i32 [0, %entry], [%iv.next, %loop]
+  %iv.next = add i32 %iv, 1
+  store i32 %iv, i32 *@G
+  %cond_1 = icmp slt i32 %iv.next, 2000
+  %widenable_cond3 = call i1 @llvm.experimental.widenable.condition()
+  %exiplicit_guard_cond4 = and i1 %cond_1, %widenable_cond3
+  br i1 %exiplicit_guard_cond4, label %loop, label %exit
+
+exit:
+  ret i32 %iv
+}
+
+ at G = external global i32
+declare i1 @llvm.experimental.widenable.condition()