[VPlan][LV] Fix invalid truncation in VPScalarIVStepsRecipe (#137832)

Replace CreateTrunc with CreateSExtOrTrunc in VPScalarIVStepsRecipe to
safely handle type conversion. This prevents assertion failures from
invalid truncation when StartIdx0 has a smaller integer type than
IntStepTy. The assertion was introduced by commit 783a846.
Fixes #137185

Author: maryammo

llvm/lib/Transforms/Vectorize/VPlanRecipes.cpp

@@ -2127,7 +2127,7 @@ void VPScalarIVStepsRecipe::execute(VPTransformState &State) {
           Builder.CreateMul(StartIdx0, ConstantInt::get(StartIdx0->getType(),
                                                         getUnrollPart(*this)));
     }
-    StartIdx0 = Builder.CreateTrunc(StartIdx0, IntStepTy);
+    StartIdx0 = Builder.CreateSExtOrTrunc(StartIdx0, IntStepTy);
   }
 
   if (!FirstLaneOnly && State.VF.isScalable()) {

llvm/test/Transforms/LoopVectorize/PowerPC/vplan-scalarivsext-crash.ll

@@ -0,0 +1,93 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -passes=loop-vectorize -S %s 2>&1 | FileCheck %s
+
+target datalayout = "E-m:a-p:32:32-Fi32-i64:64-n32"
+target triple = "powerpc-ibm-aix7.2.0.0"
+
+define void @test_iv_trunc_crash(ptr %a, ptr %b, i32 %n) {
+; CHECK-LABEL: define void @test_iv_trunc_crash(
+; CHECK-SAME: ptr [[A:%.*]], ptr [[B:%.*]], i32 [[N:%.*]]) {
+; CHECK-NEXT:  [[ENTRY:.*]]:
+; CHECK-NEXT:    [[SUM_0:%.*]] = fadd reassoc double 0.000000e+00, 0.000000e+00
+; CHECK-NEXT:    [[X:%.*]] = load double, ptr [[A]], align 8
+; CHECK-NEXT:    [[TMP0:%.*]] = sext i32 [[N]] to i64
+; CHECK-NEXT:    [[TMP1:%.*]] = add nsw i64 [[TMP0]], 1
+; CHECK-NEXT:    [[SMAX1:%.*]] = call i64 @llvm.smax.i64(i64 [[TMP1]], i64 0)
+; CHECK-NEXT:    [[TMP2:%.*]] = trunc i64 [[SMAX1]] to i32
+; CHECK-NEXT:    [[TMP3:%.*]] = add nuw i32 [[TMP2]], 1
+; CHECK-NEXT:    [[MIN_ITERS_CHECK:%.*]] = icmp ule i32 [[TMP3]], 8
+; CHECK-NEXT:    br i1 [[MIN_ITERS_CHECK]], label %[[SCALAR_PH:.*]], label %[[VECTOR_SCEVCHECK:.*]]
+; CHECK:       [[VECTOR_SCEVCHECK]]:
+; CHECK-NEXT:    [[TMP4:%.*]] = sext i32 [[N]] to i64
+; CHECK-NEXT:    [[TMP5:%.*]] = add nsw i64 [[TMP4]], 1
+; CHECK-NEXT:    [[SMAX:%.*]] = call i64 @llvm.smax.i64(i64 [[TMP5]], i64 0)
+; CHECK-NEXT:    [[TMP6:%.*]] = trunc i64 [[SMAX]] to i32
+; CHECK-NEXT:    [[TMP7:%.*]] = icmp slt i32 [[TMP6]], 0
+; CHECK-NEXT:    [[TMP8:%.*]] = icmp ugt i64 [[SMAX]], 4294967295
+; CHECK-NEXT:    [[TMP9:%.*]] = or i1 [[TMP7]], [[TMP8]]
+; CHECK-NEXT:    br i1 [[TMP9]], label %[[SCALAR_PH]], label %[[VECTOR_PH:.*]]
+; CHECK:       [[VECTOR_PH]]:
+; CHECK-NEXT:    [[N_MOD_VF:%.*]] = urem i32 [[TMP3]], 8
+; CHECK-NEXT:    [[TMP10:%.*]] = icmp eq i32 [[N_MOD_VF]], 0
+; CHECK-NEXT:    [[TMP11:%.*]] = select i1 [[TMP10]], i32 8, i32 [[N_MOD_VF]]
+; CHECK-NEXT:    [[N_VEC:%.*]] = sub i32 [[TMP3]], [[TMP11]]
+; CHECK-NEXT:    [[DOTCAST:%.*]] = sitofp i32 [[N_VEC]] to double
+; CHECK-NEXT:    [[TMP12:%.*]] = fmul reassoc double [[X]], [[DOTCAST]]
+; CHECK-NEXT:    [[TMP13:%.*]] = fadd reassoc double [[SUM_0]], [[TMP12]]
+; CHECK-NEXT:    br label %[[VECTOR_BODY:.*]]
+; CHECK:       [[VECTOR_BODY]]:
+; CHECK-NEXT:    [[INDEX:%.*]] = phi i32 [ 0, %[[VECTOR_PH]] ], [ [[INDEX_NEXT:%.*]], %[[VECTOR_BODY]] ]
+; CHECK-NEXT:    [[DOTCAST2:%.*]] = sitofp i32 [[INDEX]] to double
+; CHECK-NEXT:    [[TMP14:%.*]] = fmul reassoc double [[X]], [[DOTCAST2]]
+; CHECK-NEXT:    [[OFFSET_IDX:%.*]] = fadd reassoc double [[SUM_0]], [[TMP14]]
+; CHECK-NEXT:    [[TMP15:%.*]] = fmul reassoc double 7.000000e+00, [[X]]
+; CHECK-NEXT:    [[TMP16:%.*]] = fadd reassoc double [[OFFSET_IDX]], [[TMP15]]
+; CHECK-NEXT:    store double [[TMP16]], ptr [[B]], align 8
+; CHECK-NEXT:    [[INDEX_NEXT]] = add nuw i32 [[INDEX]], 8
+; CHECK-NEXT:    [[TMP17:%.*]] = icmp eq i32 [[INDEX_NEXT]], [[N_VEC]]
+; CHECK-NEXT:    br i1 [[TMP17]], label %[[MIDDLE_BLOCK:.*]], label %[[VECTOR_BODY]], !llvm.loop [[LOOP0:![0-9]+]]
+; CHECK:       [[MIDDLE_BLOCK]]:
+; CHECK-NEXT:    br label %[[SCALAR_PH]]
+; CHECK:       [[SCALAR_PH]]:
+; CHECK-NEXT:    [[BC_RESUME_VAL:%.*]] = phi double [ [[TMP13]], %[[MIDDLE_BLOCK]] ], [ [[SUM_0]], %[[ENTRY]] ], [ [[SUM_0]], %[[VECTOR_SCEVCHECK]] ]
+; CHECK-NEXT:    [[BC_RESUME_VAL3:%.*]] = phi i32 [ [[N_VEC]], %[[MIDDLE_BLOCK]] ], [ 0, %[[ENTRY]] ], [ 0, %[[VECTOR_SCEVCHECK]] ]
+; CHECK-NEXT:    br label %[[LOOP_HEADER:.*]]
+; CHECK:       [[LOOP_HEADER]]:
+; CHECK-NEXT:    [[SUM_1:%.*]] = phi double [ [[BC_RESUME_VAL]], %[[SCALAR_PH]] ], [ [[SUM_NEXT:%.*]], %[[LOOP_BODY:.*]] ]
+; CHECK-NEXT:    [[I:%.*]] = phi i32 [ [[BC_RESUME_VAL3]], %[[SCALAR_PH]] ], [ [[I_NEXT:%.*]], %[[LOOP_BODY]] ]
+; CHECK-NEXT:    [[COND:%.*]] = icmp sgt i32 [[I]], [[N]]
+; CHECK-NEXT:    br i1 [[COND]], label %[[EXIT:.*]], label %[[LOOP_BODY]]
+; CHECK:       [[LOOP_BODY]]:
+; CHECK-NEXT:    store double [[SUM_1]], ptr [[B]], align 8
+; CHECK-NEXT:    [[SUM_NEXT]] = fadd reassoc double [[SUM_1]], [[X]]
+; CHECK-NEXT:    [[I_NEXT]] = add i32 [[I]], 1
+; CHECK-NEXT:    br label %[[LOOP_HEADER]], !llvm.loop [[LOOP3:![0-9]+]]
+; CHECK:       [[EXIT]]:
+; CHECK-NEXT:    ret void
+;
+entry:
+  %sum.0 = fadd reassoc double 0.0, 0.0
+  %x = load double, ptr %a, align 8
+  br label %loop_header
+
+loop_header:                                      ; preds = %loop_body, %entry
+  %sum.1 = phi double [ %sum.0, %entry ], [ %sum.next, %loop_body ]
+  %i = phi i32 [ 0, %entry ], [ %i.next, %loop_body ]
+  %cond = icmp sgt i32 %i, %n
+  br i1 %cond, label %exit, label %loop_body
+
+loop_body:                                        ; preds = %loop_header
+  store double %sum.1, ptr %b, align 8
+  %sum.next = fadd reassoc double %sum.1, %x
+  %i.next = add i32 %i, 1
+  br label %loop_header
+
+exit:
+  ret void
+}
+;.
+; CHECK: [[LOOP0]] = distinct !{[[LOOP0]], [[META1:![0-9]+]], [[META2:![0-9]+]]}
+; CHECK: [[META1]] = !{!"llvm.loop.isvectorized", i32 1}
+; CHECK: [[META2]] = !{!"llvm.loop.unroll.runtime.disable"}
+; CHECK: [[LOOP3]] = distinct !{[[LOOP3]], [[META1]]}
+;.