[CodeGenPrepare] Make sure instruction get from SunkAddrs is before MemoryInst (#139303)

Function optimizeBlock may do optimizations on a block for multiple
times. In the first iteration of the loop, MemoryInst1 may generate a
sunk instruction and store it into SunkAddrs. In the second iteration of
the loop, MemoryInst2 may use the same address and then it can reuse the
sunk instruction stored in SunkAddrs, but MemoryInst2 may be before
MemoryInst1 and the corresponding sunk instruction. In order to avoid
use before def error, we need to find appropriate insert position for the
 sunk instruction.

Fixes #138208.

Author: weiguozhi

llvm/lib/CodeGen/CodeGenPrepare.cpp

@@ -5771,6 +5771,35 @@ static bool IsNonLocalValue(Value *V, BasicBlock *BB) {
   return false;
 }
 
+// Find an insert position of Addr for MemoryInst. We can't guarantee MemoryInst
+// is the first instruction that will use Addr. So we need to find the first
+// user of Addr in current BB.
+static BasicBlock::iterator findInsertPos(Value *Addr, Instruction *MemoryInst,
+                                          Value *SunkAddr) {
+  if (Addr->hasOneUse())
+    return MemoryInst->getIterator();
+
+  // We already have a SunkAddr in current BB, but we may need to insert cast
+  // instruction after it.
+  if (SunkAddr) {
+    if (Instruction *AddrInst = dyn_cast<Instruction>(SunkAddr))
+      return std::next(AddrInst->getIterator());
+  }
+
+  // Find the first user of Addr in current BB.
+  Instruction *Earliest = MemoryInst;
+  for (User *U : Addr->users()) {
+    Instruction *UserInst = dyn_cast<Instruction>(U);
+    if (UserInst && UserInst->getParent() == MemoryInst->getParent()) {
+      if (isa<PHINode>(UserInst) || UserInst->isDebugOrPseudoInst())
+        continue;
+      if (UserInst->comesBefore(Earliest))
+        Earliest = UserInst;
+    }
+  }
+  return Earliest->getIterator();
+}
+
 /// Sink addressing mode computation immediate before MemoryInst if doing so
 /// can be done without increasing register pressure.  The need for the
 /// register pressure constraint means this can end up being an all or nothing
@@ -5895,11 +5924,6 @@ bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
     return Modified;
   }
 
-  // Insert this computation right after this user.  Since our caller is
-  // scanning from the top of the BB to the bottom, reuse of the expr are
-  // guaranteed to happen later.
-  IRBuilder<> Builder(MemoryInst);
-
   // Now that we determined the addressing expression we want to use and know
   // that we have to sink it into this block.  Check to see if we have already
   // done this for some other load/store instr in this block.  If so, reuse
@@ -5910,6 +5934,13 @@ bool CodeGenPrepare::optimizeMemoryInst(Instruction *MemoryInst, Value *Addr,
 
   Value *SunkAddr = SunkAddrVH.pointsToAliveValue() ? SunkAddrVH : nullptr;
   Type *IntPtrTy = DL->getIntPtrType(Addr->getType());
+
+  // The current BB may be optimized multiple times, we can't guarantee the
+  // reuse of Addr happens later, call findInsertPos to find an appropriate
+  // insert position.
+  IRBuilder<> Builder(MemoryInst->getParent(),
+                      findInsertPos(Addr, MemoryInst, SunkAddr));
+
   if (SunkAddr) {
     LLVM_DEBUG(dbgs() << "CGP: Reusing nonlocal addrmode: " << AddrMode
                       << " for " << *MemoryInst << "\n");

llvm/test/Transforms/CodeGenPrepare/X86/sink-addr-reuse.ll

@@ -0,0 +1,44 @@
+; NOTE: Assertions have been autogenerated by utils/update_test_checks.py UTC_ARGS: --version 5
+; RUN: opt -S -p 'require<profile-summary>,codegenprepare' -cgpp-huge-func=0 < %s | FileCheck %s
+
+target datalayout = "e-m:e-p270:32:32-p271:32:32-p272:64:64-i64:64-i128:128-f80:128-n8:16:32:64-S128"
+target triple = "x86_64-grtev4-linux-gnu"
+
+declare void @g(ptr)
+
+; %load and %load5 use the same address, %load5 is optimized first, %load is
+; optimized later and reuse the same address computation instruction. We must
+; make sure not to generate use before def error.
+
+define void @f(ptr %arg) {
+; CHECK-LABEL: define void @f(
+; CHECK-SAME: ptr [[ARG:%.*]]) {
+; CHECK-NEXT:  [[BB:.*:]]
+; CHECK-NEXT:    [[GETELEMENTPTR:%.*]] = getelementptr i8, ptr [[ARG]], i64 -64
+; CHECK-NEXT:    call void @g(ptr [[GETELEMENTPTR]])
+; CHECK-NEXT:    [[SUNKADDR1:%.*]] = getelementptr i8, ptr [[ARG]], i64 -64
+; CHECK-NEXT:    [[LOAD:%.*]] = load ptr, ptr [[SUNKADDR1]], align 8
+; CHECK-NEXT:    [[SUNKADDR:%.*]] = getelementptr i8, ptr [[ARG]], i64 -56
+; CHECK-NEXT:    [[LOAD4:%.*]] = load i32, ptr [[SUNKADDR]], align 8
+; CHECK-NEXT:    [[LOAD5:%.*]] = load ptr, ptr [[SUNKADDR1]], align 8
+; CHECK-NEXT:    [[TMP0:%.*]] = call { i32, i1 } @llvm.uadd.with.overflow.i32(i32 1, i32 0)
+; CHECK-NEXT:    [[MATH:%.*]] = extractvalue { i32, i1 } [[TMP0]], 0
+; CHECK-NEXT:    ret void
+;
+bb:
+  %getelementptr = getelementptr i8, ptr %arg, i64 -64
+  %getelementptr1 = getelementptr i8, ptr %arg, i64 -56
+  call void @g(ptr %getelementptr)
+  br label %bb3
+
+bb3:
+  %load = load ptr, ptr %getelementptr, align 8
+  %load4 = load i32, ptr %getelementptr1, align 8
+  %load5 = load ptr, ptr %getelementptr, align 8
+  %add = add i32 1, 0
+  %icmp = icmp eq i32 %add, 0
+  br i1 %icmp, label %bb7, label %bb7
+
+bb7:
+  ret void
+}