[llvm] [SCEV] Simplify SCEVExpr for PHI to SCEV for operand if operands are identical (PR #115945)

[Nikita Popov via llvm-commits]

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@@ -0,0 +1,46 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -disable-output "-passes=print<scalar-evolution>" 2>&1 | FileCheck %s
+define void @test(ptr %x, ptr %y) {
+; CHECK-LABEL: 'test'
+; CHECK-NEXT:  Classifying expressions for: @test
+; CHECK-NEXT:    %v1.0 = phi i32 [ 0, %entry ], [ %k.0, %if.end ]
+; CHECK-NEXT:    --> {0,+,1}<nuw><nsw><%for.cond> U: [0,7) S: [0,7) Exits: 6 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT:    %add = add nsw i32 %v1.0, 1
+; CHECK-NEXT:    --> {1,+,1}<nuw><nsw><%for.cond> U: [1,8) S: [1,8) Exits: 7 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT:    %add6 = add nsw i32 %v1.0, 1
+; CHECK-NEXT:    --> {1,+,1}<nuw><nsw><%for.cond> U: [1,8) S: [1,8) Exits: 7 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT:    %k.0 = phi i32 [ %add, %if.then ], [ %add6, %if.else ]
+; CHECK-NEXT:    --> {1,+,1}<nuw><nsw><%for.cond> U: [1,8) S: [1,8) Exits: 7 LoopDispositions: { %for.cond: Computable }
+; CHECK-NEXT:  Determining loop execution counts for: @test
+; CHECK-NEXT:  Loop %for.cond: backedge-taken count is i32 6
+; CHECK-NEXT:  Loop %for.cond: constant max backedge-taken count is i32 6
+; CHECK-NEXT:  Loop %for.cond: symbolic max backedge-taken count is i32 6
+; CHECK-NEXT:  Loop %for.cond: Trip multiple is 7
+;
+entry:
+  br label %for.cond
+
+for.cond:                                                ; preds = %6, %0
+  %v1.0 = phi i32 [ 0, %entry ], [ %k.0, %if.end ]
+  %cmp = icmp slt i32 %v1.0, 6
+  br i1 %cmp, label %for.body, label %exit
+
+for.body:                                                ; preds = %1
+  %cmp3 = icmp slt i32 %v1.0, 2
+  br i1 %cmp3, label %if.then, label %if.else
+
+if.then:                                                ; preds = %2
+  %add = add nsw i32 %v1.0, 1
+  br label %if.end
+
+if.else:                                                ; preds = %2
+  %add6 = add nsw i32 %v1.0, 1
+  br label %if.end
+
+if.end:                                                ; preds = %4, %3
+  %k.0 = phi i32 [ %add, %if.then ], [ %add6, %if.else ]
+  br label %for.cond
+
+exit:                                                ; preds = %5
+  ret void
+}
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nikic wrote:

Can you please add a test variant where the adds have different flags (e.g. one nsw one nuw) to show it still works?

https://github.com/llvm/llvm-project/pull/115945