[BOLT][AArch64] Fix search to proceed upwards from memcpy call (#166182)

The search should proceed from CallInst to the beginning of BB since X2
can be rewritten and we need to catch the most recent write before the
call.

Patch by Yafet Beyene alulayafet@gmail.com

Author: ElvinaYakubova

bolt/lib/Target/AArch64/AArch64MCPlusBuilder.cpp

@@ -2804,7 +2804,7 @@ class AArch64MCPlusBuilder : public MCPlusBuilder {
     BitVector WrittenRegs(RegInfo->getNumRegs());
     const BitVector &SizeRegAliases = getAliases(SizeReg);
 
-    for (auto InstIt = BB.begin(); InstIt != CallInst; ++InstIt) {
+    for (auto InstIt = CallInst; InstIt != BB.begin(); --InstIt) {
       const MCInst &Inst = *InstIt;
       WrittenRegs.reset();
       getWrittenRegs(Inst, WrittenRegs);

bolt/test/runtime/AArch64/inline-memcpy.s

@@ -7,7 +7,7 @@
 # RUN: llvm-bolt %t.exe --inline-memcpy -o %t.bolt 2>&1 | FileCheck %s --check-prefix=CHECK-INLINE
 # RUN: llvm-objdump -d %t.bolt | FileCheck %s --check-prefix=CHECK-ASM
 
-# Verify BOLT reports that it inlined memcpy calls (11 successful inlines out of 16 total calls)
+# Verify BOLT reports that it inlined memcpy calls (11 successful inlines out of 17 total calls)
 # CHECK-INLINE: BOLT-INFO: inlined 11 memcpy() calls
 
 # Each function should use optimal size-specific instructions and NO memcpy calls
@@ -84,6 +84,9 @@
 # CHECK-ASM-LABEL: <test_register_move_negative>:
 # CHECK-ASM: bl{{.*}}<memcpy
 
+# CHECK-ASM-LABEL: <test_x2_rewrite_negative>:
+# CHECK-ASM: bl{{.*}}<memcpy
+
 # Live-in parameter should NOT be inlined (size unknown at compile time)
 # CHECK-ASM-LABEL: <test_live_in_negative>:
 # CHECK-ASM: bl{{.*}}<memcpy
@@ -273,6 +276,15 @@ test_register_move_negative:
 	ret
 	.size	test_register_move_negative, .-test_register_move_negative
 
+	.globl  test_x2_rewrite_negative
+	.type   test_x2_rewrite_negative,@function
+test_x2_rewrite_negative:
+	mov     x2, #8
+	ldr     x2, [sp, #24]
+	bl      memcpy
+	ret
+	.size   test_x2_rewrite_negative, .-test_x2_rewrite_negative
+
 	.globl	test_live_in_negative
 	.type	test_live_in_negative,@function
 test_live_in_negative: