[llvm] [InstCombine] limit icmp sgt (shl nsw X, C1), C0 --> icmp sgt X, C0 >> C1 to hasOneUse (PR #74318)

[via llvm-commits]

================
@@ -0,0 +1,53 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: opt -S -passes='instcombine,indvars'  < %s | FileCheck %s
+
+target datalayout = "e-m:e-p:64:64-i64:64-i128:128-n32:64-S128"
+
+define void @g(ptr nocapture noundef %a, i32 noundef signext %n) {
+; CHECK-LABEL: @g(
+; CHECK-NEXT:  entry:
+; CHECK-NEXT:    [[MUL:%.*]] = shl nsw i32 [[N:%.*]], 4
+; CHECK-NEXT:    [[CMP11:%.*]] = icmp sgt i32 [[MUL]], 0
+; CHECK-NEXT:    br i1 [[CMP11]], label [[FOR_BODY_PREHEADER:%.*]], label [[FOR_COND_CLEANUP:%.*]]
+; CHECK:       for.body.preheader:
+; CHECK-NEXT:    [[WIDE_TRIP_COUNT:%.*]] = zext i32 [[MUL]] to i64
+; CHECK-NEXT:    br label [[FOR_BODY:%.*]]
+; CHECK:       for.cond.cleanup.loopexit:
+; CHECK-NEXT:    br label [[FOR_COND_CLEANUP]]
+; CHECK:       for.cond.cleanup:
+; CHECK-NEXT:    ret void
+; CHECK:       for.body:
+; CHECK-NEXT:    [[INDVARS_IV:%.*]] = phi i64 [ [[INDVARS_IV_NEXT:%.*]], [[FOR_BODY]] ], [ 0, [[FOR_BODY_PREHEADER]] ]
+; CHECK-NEXT:    [[ARRAYIDX:%.*]] = getelementptr inbounds i32, ptr [[A:%.*]], i64 [[INDVARS_IV]]
+; CHECK-NEXT:    [[TMP0:%.*]] = load i32, ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[ADD:%.*]] = shl nsw i32 [[TMP0]], 1
+; CHECK-NEXT:    store i32 [[ADD]], ptr [[ARRAYIDX]], align 4
+; CHECK-NEXT:    [[INDVARS_IV_NEXT]] = add nuw nsw i64 [[INDVARS_IV]], 1
+; CHECK-NEXT:    [[EXITCOND:%.*]] = icmp ne i64 [[INDVARS_IV_NEXT]], [[WIDE_TRIP_COUNT]]
+; CHECK-NEXT:    br i1 [[EXITCOND]], label [[FOR_BODY]], label [[FOR_COND_CLEANUP_LOOPEXIT:%.*]]
+;
+entry:
+  %mul = shl nsw i32 %n, 4
+  %cmp11 = icmp sgt i32 %mul, 0
+  br i1 %cmp11, label %for.body.preheader, label %for.cond.cleanup
+
+for.body.preheader:                               ; preds = %entry
+  br label %for.body
+
+for.cond.cleanup.loopexit:                        ; preds = %for.body
+  br label %for.cond.cleanup
+
+for.cond.cleanup:                                 ; preds = %for.cond.cleanup.loopexit, %entry
+  ret void
+
+for.body:                                         ; preds = %for.body.preheader, %for.body
+  %i.012 = phi i32 [ %inc, %for.body ], [ 0, %for.body.preheader ]
+  %idxprom = zext nneg i32 %i.012 to i64
+  %arrayidx = getelementptr inbounds i32, ptr %a, i64 %idxprom
+  %0 = load i32, ptr %arrayidx, align 4
+  %add = shl nsw i32 %0, 1
+  store i32 %add, ptr %arrayidx, align 4
+  %inc = add nuw nsw i32 %i.012, 1
+  %cmp = icmp slt i32 %inc, %mul
+  br i1 %cmp, label %for.body, label %for.cond.cleanup.loopexit
+}
----------------
goldsteinn wrote:

Err Im sorry, I was unclear. I mean can you just split it into two commits?
I.e 
commit 1: add new tests
commit 2: impl + update tests.

An example might be: https://github.com/llvm/llvm-project/pull/83739/commits

https://github.com/llvm/llvm-project/pull/74318