[llvm] [SCEV] Infer loop max trip count from memory accesses (PR #70361)

[Johannes Doerfert via llvm-commits]

================
@@ -0,0 +1,191 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py
+; RUN: opt < %s -disable-output "-passes=print<scalar-evolution>" -scalar-evolution-classify-expressions=0 -scalar-evolution-infer-max-trip-count-from-memory-access 2>&1 | FileCheck %s
+
+define void @ComputeMaxTripCountFromArrayNormal(i32 signext %len) {
+; CHECK-LABEL: 'ComputeMaxTripCountFromArrayNormal'
+; CHECK-NEXT:  Determining loop execution counts for: @ComputeMaxTripCountFromArrayNormal
+; CHECK-NEXT:  Loop %for.body: backedge-taken count is (-1 + %len)
+; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is 2147483646
+; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is (-1 + %len)
+; CHECK-NEXT:  Loop %for.body: Predicated backedge-taken count is (-1 + %len)
+; CHECK-NEXT:   Predicates:
+; CHECK:       Loop %for.body: Trip multiple is 1
+; CHECK-NEXT:  Loop %for.body: Small constant max trip is 8
+;
+entry:
+  %a = alloca [7 x i32], align 4
+  %cmp4 = icmp sgt i32 %len, 0
+  br i1 %cmp4, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:
+  br label %for.body
+
+for.cond.cleanup.loopexit:
+  br label %for.cond.cleanup
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %iv = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %idxprom = zext i32 %iv to i64
+  %arrayidx = getelementptr inbounds [7 x i32], [7 x i32]* %a, i64 0, i64 %idxprom
+  store i32 0, i32* %arrayidx, align 4
+  %inc = add nuw nsw i32 %iv, 1
+  %cmp = icmp slt i32 %inc, %len
+  br i1 %cmp, label %for.body, label %for.cond.cleanup.loopexit
+}
+
+
+define void @ComputeMaxTripCountFromZeroArray(i32 signext %len) {
+; CHECK-LABEL: 'ComputeMaxTripCountFromZeroArray'
+; CHECK-NEXT:  Determining loop execution counts for: @ComputeMaxTripCountFromZeroArray
+; CHECK-NEXT:  Loop %for.body: backedge-taken count is (-1 + %len)
+; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is 2147483646
+; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is (-1 + %len)
+; CHECK-NEXT:  Loop %for.body: Predicated backedge-taken count is (-1 + %len)
+; CHECK-NEXT:   Predicates:
+; CHECK:       Loop %for.body: Trip multiple is 1
+; CHECK-NEXT:  Loop %for.body: Small constant max trip is 1
+;
+entry:
+  %a = alloca [0 x i32], align 4
+  %cmp4 = icmp sgt i32 %len, 0
+  br i1 %cmp4, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:
+  br label %for.body
+
+for.cond.cleanup.loopexit:
+  br label %for.cond.cleanup
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %iv = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %idxprom = zext i32 %iv to i64
+  %arrayidx = getelementptr inbounds [0 x i32], [0 x i32]* %a, i64 0, i64 %idxprom
+  store i32 0, i32* %arrayidx, align 4
+  %inc = add nuw nsw i32 %iv, 1
+  %cmp = icmp slt i32 %inc, %len
+  br i1 %cmp, label %for.body, label %for.cond.cleanup.loopexit
+}
+
+define void @ComputeMaxTripCountFromExtremArray(i32 signext %len) {
+; CHECK-LABEL: 'ComputeMaxTripCountFromExtremArray'
+; CHECK-NEXT:  Determining loop execution counts for: @ComputeMaxTripCountFromExtremArray
+; CHECK-NEXT:  Loop %for.body: backedge-taken count is (-1 + %len)
+; CHECK-NEXT:  Loop %for.body: constant max backedge-taken count is 2147483646
+; CHECK-NEXT:  Loop %for.body: symbolic max backedge-taken count is (-1 + %len)
+; CHECK-NEXT:  Loop %for.body: Predicated backedge-taken count is (-1 + %len)
+; CHECK-NEXT:   Predicates:
+; CHECK:       Loop %for.body: Trip multiple is 1
+; CHECK-NEXT:  Loop %for.body: Small constant max trip is 2147483647
+;
+entry:
+  %a = alloca [4294967295 x i1], align 4
+  %cmp4 = icmp sgt i32 %len, 0
+  br i1 %cmp4, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:
+  br label %for.body
+
+for.cond.cleanup.loopexit:
+  br label %for.cond.cleanup
+
+for.cond.cleanup:
+  ret void
+
+for.body:
+  %iv = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %idxprom = zext i32 %iv to i64
+  %arrayidx = getelementptr inbounds [4294967295 x i1], [4294967295 x i1]* %a, i64 0, i64 %idxprom
+  store i1 0, i1* %arrayidx, align 4
+  %inc = add nuw nsw i32 %iv, 1
+  %cmp = icmp slt i32 %inc, %len
+  br i1 %cmp, label %for.body, label %for.cond.cleanup.loopexit
+}
+
+
+define void @ComputeMaxTripCountFromArrayInBranch(i32 signext %len) {
+; CHECK-LABEL: 'ComputeMaxTripCountFromArrayInBranch'
+; CHECK-NEXT:  Determining loop execution counts for: @ComputeMaxTripCountFromArrayInBranch
+; CHECK-NEXT:  Loop %for.cond: backedge-taken count is (0 smax %len)
+; CHECK-NEXT:  Loop %for.cond: constant max backedge-taken count is 2147483647
+; CHECK-NEXT:  Loop %for.cond: symbolic max backedge-taken count is (0 smax %len)
+; CHECK-NEXT:  Loop %for.cond: Predicated backedge-taken count is (0 smax %len)
+; CHECK-NEXT:   Predicates:
+; CHECK:       Loop %for.cond: Trip multiple is 1
+; CHECK-NEXT:  Loop %for.cond: Small constant max trip is 2147483648
+;
+entry:
+  %a = alloca [8 x i32], align 4
+  br label %for.cond
+
+for.cond:
+  %iv = phi i32 [ %inc, %for.inc ], [ 0, %entry ]
+  %cmp = icmp slt i32 %iv, %len
+  br i1 %cmp, label %for.body, label %for.cond.cleanup
+
+for.cond.cleanup:
+  br label %for.end
+
+for.body:
+  %cmp1 = icmp slt i32 %iv, 8
+  br i1 %cmp1, label %if.then, label %if.end
+
+if.then:
+  %idxprom = sext i32 %iv to i64
+  %arrayidx = getelementptr inbounds [8 x i32], [8 x i32]* %a, i64 0, i64 %idxprom
+  store i32 0, i32* %arrayidx, align 4
+  br label %if.end
+
+if.end:
+  br label %for.inc
+
+for.inc:
+  %inc = add nsw i32 %iv, 1
+  br label %for.cond
+
+for.end:
+  ret void
+}
+
+define void @ComputeMaxTripCountFromMultiDemArray(i32 signext %len) {
----------------
jdoerfert wrote:

-Dem +Dim

https://github.com/llvm/llvm-project/pull/70361