Adding a test showing the current state of poor code gen of search loop

[avt77]

Summary

PR27136 shows failure to hoist constant out of loop. This test is used as start point to fix the failure: it shows the current state of codegen and discovers what should be fixed

[RKSimon]

LGTM

test/CodeGen/X86/loop-search.ll

+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py
+; RUN: llc < %s -mtriple=x86_64-apple-darwin | FileCheck %s
+
+; This test comes from PR27136
+; We should hoist loop constant invariant
+
+define zeroext i1 @search(i32 %needle, i32* nocapture readonly %haystack, i32 %count) {
+; CHECK-LABEL: search:
+; CHECK:       ## BB#0: ## %entry
+; CHECK-NEXT:    testl %edx, %edx
+; CHECK-NEXT:    jle LBB0_1
+; CHECK-NEXT:  ## BB#4: ## %for.body.preheader
+; CHECK-NEXT:    movslq %edx, %rcx
+; CHECK-NEXT:    xorl %edx, %edx
+; CHECK-NEXT:    .p2align 4, 0x90
+; CHECK-NEXT:  LBB0_5: ## %for.body
+; CHECK-NEXT:    ## =>This Inner Loop Header: Depth=1
+;            ### FIXME: This loop invariant should be hoisted
+; CHECK-NEXT:    movb $1, %al
+; CHECK-NEXT:    cmpl %edi, (%rsi,%rdx,4)
+; CHECK-NEXT:    je LBB0_6
+; CHECK-NEXT:  ## BB#2: ## %for.cond
+; CHECK-NEXT:    ## in Loop: Header=BB0_5 Depth=1
+; CHECK-NEXT:    incq %rdx
+; CHECK-NEXT:    cmpq %rcx, %rdx
+; CHECK-NEXT:    jl LBB0_5
+;            ### FIXME: BB#3 and LBB0_1 should be merged
+; CHECK-NEXT:  ## BB#3:
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    ## kill: %AL<def> %AL<kill> %EAX<kill>
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  LBB0_1:
+; CHECK-NEXT:    xorl %eax, %eax
+; CHECK-NEXT:    ## kill: %AL<def> %AL<kill> %EAX<kill>
+; CHECK-NEXT:    retq
+; CHECK-NEXT:  LBB0_6: ## %cleanup
+; CHECK-NEXT:    ## kill: %AL<def> %AL<kill> %EAX<kill>
+; CHECK-NEXT:    retq
+;
+entry:
+  %cmp5 = icmp sgt i32 %count, 0
+  br i1 %cmp5, label %for.body.preheader, label %cleanup
+
+for.body.preheader:                               ; preds = %entry
+  %0 = sext i32 %count to i64
+  br label %for.body
+
+for.cond:                                         ; preds = %for.body
+  %cmp = icmp slt i64 %indvars.iv.next, %0
+  br i1 %cmp, label %for.body, label %cleanup.loopexit
+
+for.body:                                         ; preds = %for.body.preheader, %for.cond
+  %indvars.iv = phi i64 [ 0, %for.body.preheader ], [ %indvars.iv.next, %for.cond ]
+  %arrayidx = getelementptr inbounds i32, i32* %haystack, i64 %indvars.iv
+  %1 = load i32, i32* %arrayidx, align 4
+  %cmp1 = icmp eq i32 %1, %needle
+  %indvars.iv.next = add nuw nsw i64 %indvars.iv, 1
+  br i1 %cmp1, label %cleanup.loopexit, label %for.cond
+
+cleanup.loopexit:                                 ; preds = %for.cond, %for.body
+  %.ph = phi i1 [ false, %for.cond ], [ true, %for.body ]
+  br label %cleanup
+
+cleanup:                                          ; preds = %cleanup.loopexit, %entry
+  %2 = phi i1 [ false, %entry ], [ %.ph, %cleanup.loopexit ]
+  ret i1 %2
+}