[llvm] [AMDGPU] Add the missing insertion point before IRBuilder instruction creation (PR #165315)

[Changpeng Fang via llvm-commits]

https://github.com/changpeng created https://github.com/llvm/llvm-project/pull/165315

  Should set the insertion point appropriately before we create an instruction with IRBuilder.

Fixes: SWDEV-562571

>From a7b82716b510ad7a0901ff577576f0a314140130 Mon Sep 17 00:00:00 2001
From: Changpeng Fang <changpeng.fang at amd.com>
Date: Mon, 27 Oct 2025 13:14:14 -0700
Subject: [PATCH] [AMDGPU] Add the missing insert point before IRBuilder
 instructiin creation

  Should set the insertion point appropriately before we create an instruction
with IRBuilder.

Fixes: SWDEV-562571
---
 .../InstCombineSimplifyDemanded.cpp           |  2 ++
 .../InstCombine/fold-selective-shift.ll       | 22 +++++++++++++++++++
 2 files changed, 24 insertions(+)

diff --git a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
index 651e305f57dfc..550dfc57a348b 100644
--- a/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
+++ b/llvm/lib/Transforms/InstCombine/InstCombineSimplifyDemanded.cpp
@@ -105,6 +105,8 @@ static Value *simplifyShiftSelectingPackedElement(Instruction *I,
   if (~KnownShrBits.Zero != ShlAmt)
     return nullptr;
 
+  IRBuilderBase::InsertPointGuard Guard(IC.Builder);
+  IC.Builder.SetInsertPoint(I);
   Value *ShrAmtZ =
       IC.Builder.CreateICmpEQ(ShrAmt, Constant::getNullValue(ShrAmt->getType()),
                               ShrAmt->getName() + ".z");
diff --git a/llvm/test/Transforms/InstCombine/fold-selective-shift.ll b/llvm/test/Transforms/InstCombine/fold-selective-shift.ll
index 2b2296541f14a..dcfd93328e087 100644
--- a/llvm/test/Transforms/InstCombine/fold-selective-shift.ll
+++ b/llvm/test/Transforms/InstCombine/fold-selective-shift.ll
@@ -21,6 +21,28 @@ define i16 @selective_shift_16(i32 %mask, i16 %upper, i16 %lower) {
   ret i16 %trunc
 }
 
+; Will assert if InsertPoint is not set before creating an instruction
+; with IRBuilder
+define i16 @selective_shift_16_insertpt(i32 %mask, i16 %upper, i16 %lower) {
+; CHECK-LABEL: define i16 @selective_shift_16_insertpt(
+; CHECK-SAME: i32 [[MASK:%.*]], i16 [[UPPER:%.*]], i16 [[LOWER:%.*]]) {
+; CHECK-NEXT:    [[MASK_BIT:%.*]] = and i32 [[MASK]], 16
+; CHECK-NEXT:    [[MASK_BIT_Z:%.*]] = icmp eq i32 [[MASK_BIT]], 0
+; CHECK-NEXT:    [[SEL_V:%.*]] = select i1 [[MASK_BIT_Z]], i16 [[LOWER]], i16 [[UPPER]]
+; CHECK-NEXT:    [[ADD_ONE:%.*]] = add i16 [[SEL_V]], 1
+; CHECK-NEXT:    ret i16 [[ADD_ONE]]
+;
+  %mask.bit = and i32 %mask, 16
+  %upper.zext = zext i16 %upper to i32
+  %upper.shl = shl nuw i32 %upper.zext, 16
+  %lower.zext = zext i16 %lower to i32
+  %pack = or disjoint i32 %upper.shl, %lower.zext
+  %sel = lshr i32 %pack, %mask.bit
+  %add.one = add i32 %sel, 1
+  %trunc = trunc i32 %add.one to i16
+  ret i16 %trunc
+}
+
 define i16 @selective_shift_16.commute(i32 %mask, i16 %upper, i16 %lower) {
 ; CHECK-LABEL: define i16 @selective_shift_16.commute(
 ; CHECK-SAME: i32 [[MASK:%.*]], i16 [[UPPER:%.*]], i16 [[LOWER:%.*]]) {