SCEV, IndVarSimplify: add samesign test from a regression

While attempting to teach ScalarEvolution about samesign in another
effort, a complicated testcase with nested loops, and zero-extends of
the induction-variable regresses, but only when the target datalayout is
present. The regression was originally reported on IndVarSimplify, but
an improvement of symbolic BTC was also observed on SCEV. Check in the
test into both IndVarSimplify and SCEV, to ease investigation and
further development.

Author: artagnon

llvm/test/Analysis/ScalarEvolution/exit-count-samesign.ll

@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_analyze_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -disable-output "-passes=print<scalar-evolution>" \
+; RUN:  -scalar-evolution-classify-expressions=0 < %s 2>&1 | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+
+define i32 @exit_count_samesign(i32 %iter.count, ptr %ptr) {
+; CHECK-LABEL: 'exit_count_samesign'
+; CHECK-NEXT:  Determining loop execution counts for: @exit_count_samesign
+; CHECK-NEXT:  Loop %inner.loop: backedge-taken count is (-1 + (1 smax {(-1 + %iter.count)<nsw>,+,-1}<nsw><%outer.loop>))<nsw>
+; CHECK-NEXT:  Loop %inner.loop: constant max backedge-taken count is i32 2147483646
+; CHECK-NEXT:  Loop %inner.loop: symbolic max backedge-taken count is (-1 + (1 smax {(-1 + %iter.count)<nsw>,+,-1}<nsw><%outer.loop>))<nsw>
+; CHECK-NEXT:  Loop %inner.loop: Trip multiple is 1
+; CHECK-NEXT:  Loop %outer.loop: <multiple exits> Unpredictable backedge-taken count.
+; CHECK-NEXT:  Loop %outer.loop: Unpredictable constant max backedge-taken count.
+; CHECK-NEXT:  Loop %outer.loop: Unpredictable symbolic max backedge-taken count.
+;
+entry:
+  br label %outer.loop
+
+ph:
+  br label %outer.loop
+
+outer.loop:
+  %iv.outer = phi i32 [ %iv.outer.1, %ph ], [ %iter.count, %entry ]
+  %iv.outer.1 = add nsw i32 %iv.outer, -1
+  %ext.outer = zext nneg i32 %iv.outer.1 to i64
+  %gep.outer = getelementptr double, ptr %ptr, i64 %ext.outer
+  store double poison, ptr %gep.outer
+  %exit.cond.outer = icmp samesign ugt i32 %iv.outer, 1
+  br i1 %exit.cond.outer, label %inner.loop, label %ph
+
+inner.loop:
+  %iv.inner = phi i32 [ %iv.next, %inner.loop ], [ 0, %outer.loop ]
+  %ext.inner = zext nneg i32 %iv.inner to i64
+  %gep.inner = getelementptr double, ptr %ptr, i64 %ext.inner
+  store double poison, ptr %gep.inner
+  %iv.next = add nuw nsw i32 %iv.inner, 1
+  %exit.cond.inner = icmp slt i32 %iv.next, %iv.outer.1
+  br i1 %exit.cond.inner, label %inner.loop, label %ph
+
+exit:
+  ret i32 0
+}

llvm/test/Transforms/IndVarSimplify/iv-zext-samesign.ll

@@ -0,0 +1,62 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt < %s -passes=indvars -S | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+
+define i32 @iv_zext_samesign(i32 %iter.count, ptr %ptr) {
+; CHECK-LABEL: define i32 @iv_zext_samesign(
+; CHECK-SAME: i32 [[ITER_COUNT:%.*]], ptr [[PTR:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[ITER_COUNT]] to i64
+; CHECK-NEXT:    br label %[[OUTER_LOOP:.*]]
+; CHECK:       [[PH_LOOPEXIT:.*]]:
+; CHECK-NEXT:    br label %[[PH:.*]]
+; CHECK:       [[PH]]:
+; CHECK-NEXT:    br label %[[OUTER_LOOP]]
+; CHECK:       [[OUTER_LOOP]]:
+; CHECK-NEXT:    [[INDVARS_IV1:%.*]] = phi i64 [ [[INDVARS_IV_NEXT2:%.*]], %[[PH]] ], [ [[TMP0]], %[[ENTRY]] ]
+; CHECK-NEXT:    [[INDVARS_IV_NEXT2]] = add nsw i64 [[INDVARS_IV1]], -1
+; CHECK-NEXT:    [[GEP_OUTER:%.*]] = getelementptr double, ptr [[PTR]], i64 [[INDVARS_IV_NEXT2]]
+; CHECK-NEXT:    store double poison, ptr [[GEP_OUTER]], align 8
+; CHECK-NEXT:    [[TMP1:%.*]] = trunc nsw i64 [[INDVARS_IV1]] to i32
+; CHECK-NEXT:    [[EXIT_COND_OUTER:%.*]] = icmp samesign ugt i32 [[TMP1]], 1
+; CHECK-NEXT:    br i1 [[EXIT_COND_OUTER]], label %[[INNER_LOOP_PREHEADER:.*]], label %[[PH]]
+; CHECK:       [[INNER_LOOP_PREHEADER]]:
+; CHECK-NEXT:    br label %[[INNER_LOOP:.*]]
+; CHECK:       [[INNER_LOOP]]:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ 0, %[[INNER_LOOP_PREHEADER]] ], [ [[INDVARS_IV_NEXT:%.*]], %[[INNER_LOOP]] ]
+; CHECK-NEXT:    [[GEP_INNER:%.*]] = getelementptr double, ptr [[PTR]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    store double poison, ptr [[GEP_INNER]], align 8
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXIT_COND_INNER:%.*]] = icmp slt i64 [[INDVARS_IV_NEXT]], [[INDVARS_IV_NEXT2]]
+; CHECK-NEXT:    br i1 [[EXIT_COND_INNER]], label %[[INNER_LOOP]], label %[[PH_LOOPEXIT]]
+; CHECK:       [[EXIT:.*:]]
+; CHECK-NEXT:    ret i32 0
+;
+entry:
+  br label %outer.loop
+
+ph:
+  br label %outer.loop
+
+outer.loop:
+  %iv.outer = phi i32 [ %iv.outer.1, %ph ], [ %iter.count, %entry ]
+  %iv.outer.1 = add nsw i32 %iv.outer, -1
+  %ext.outer = zext nneg i32 %iv.outer.1 to i64
+  %gep.outer = getelementptr double, ptr %ptr, i64 %ext.outer
+  store double poison, ptr %gep.outer
+  %exit.cond.outer = icmp samesign ugt i32 %iv.outer, 1
+  br i1 %exit.cond.outer, label %inner.loop, label %ph
+
+inner.loop:
+  %iv.inner = phi i32 [ %iv.next, %inner.loop ], [ 0, %outer.loop ]
+  %ext.inner = zext nneg i32 %iv.inner to i64
+  %gep.inner = getelementptr double, ptr %ptr, i64 %ext.inner
+  store double poison, ptr %gep.inner
+  %iv.next = add nuw nsw i32 %iv.inner, 1
+  %exit.cond.inner = icmp slt i32 %iv.next, %iv.outer.1
+  br i1 %exit.cond.inner, label %inner.loop, label %ph
+
+exit:
+  ret i32 0
+}