From 5d659bdc94338f53797cc0ad34e2a77c2bfb3e66 Mon Sep 17 00:00:00 2001
From: Zoe Carver <z.zoelec2@gmail.com>
Date: Thu, 15 Oct 2020 19:08:32 -0700
Subject: [PATCH] Move insert point after PHI nodes. (#794)

If replacing a PHI node with another instruction, make sure the
insertion point is after the last PHI node in that block. This prevents
the assertion described in #779.
---
 lib/Codegen/Codegen.cpp        | 11 ++++++++
 test/Pass/insert-after-phis.ll | 46 ++++++++++++++++++++++++++++++++++
 2 files changed, 57 insertions(+)
 create mode 100644 test/Pass/insert-after-phis.ll

diff --git a/lib/Codegen/Codegen.cpp b/lib/Codegen/Codegen.cpp
index 920631457..75fa3e52f 100644
--- a/lib/Codegen/Codegen.cpp
+++ b/lib/Codegen/Codegen.cpp
@@ -99,6 +99,17 @@ llvm::Value *Codegen::getValue(Inst *I) {
   if (!V0)
     return nullptr;
 
+  // PHI nodes must be the first instructions in a basic block. If we're
+  // replacing a PHI node with another instruction, make sure it comes after the
+  // other PHI nodes.
+  if (ReplacedInst &&
+      isa<PHINode>(ReplacedInst->getNextNode())) {
+    Instruction *InsertPoint = ReplacedInst;
+    while (isa<PHINode>(InsertPoint))
+      InsertPoint = InsertPoint->getNextNode();
+    Builder.SetInsertPoint(InsertPoint->getNextNode());
+  }
+
   switch (Ops.size()) {
   case 1: {
     switch (I->K) {
diff --git a/test/Pass/insert-after-phis.ll b/test/Pass/insert-after-phis.ll
new file mode 100644
index 000000000..33dd6ed7f
--- /dev/null
+++ b/test/Pass/insert-after-phis.ll
@@ -0,0 +1,46 @@
+; RUN: %opt -load %pass -souper -S -stats -o - %s 2>&1 | %FileCheck %s
+
+; The main thing being tested here is just that the verifier doesn't error
+; because a PHI node comes after another instruction.
+
+@c = local_unnamed_addr global i32 0, align 4
+@d = local_unnamed_addr global i32 0, align 4
+@e = local_unnamed_addr global i64 0, align 8
+@b = local_unnamed_addr global i32 0, align 4
+@a = global [1 x i32] zeroinitializer, align 4
+@f = global [1 x i32] zeroinitializer, align 4
+
+; CHECK: define void @g()
+define void @g() {
+entry:
+  br i1 icmp ule (i32* getelementptr inbounds ([1 x i32], [1 x i32]* @a, i64 0, i64 0), i32* inttoptr (i64 6 to i32*)), label %for.body.lr.ph, label %for.end14
+
+for.body.lr.ph:
+  %b.promoted = load i32, i32* @b, align 4
+  %e.promoted = load i64, i64* @e, align 8
+  br label %for.inc10
+
+for.inc10:
+  %0 = sub nuw nsw i32 1, %b.promoted
+  %cmp = icmp sge i32 %b.promoted, 0
+  br i1 %cmp, label %for.inc10, label %for.inc13
+
+for.inc13:
+  %.lcssa = phi i32 [ %0, %for.inc10 ]
+  %dec.6.lcssa = phi i64 [ %e.promoted, %for.inc10 ]
+  %inc = add nsw i32 %b.promoted, 1
+  br i1 icmp ule (i32* getelementptr inbounds ([1 x i32], [1 x i32]* @a, i64 0, i64 0), i32* inttoptr (i64 6 to i32*)), label %for.inc10, label %for.cond.for.end14_crit_edge
+
+for.cond.for.end14_crit_edge:
+  %.lcssa.lcssa = phi i32 [ %.lcssa, %for.inc13 ]
+  %dec.6.lcssa.lcssa = phi i64 [ %dec.6.lcssa, %for.inc13 ]
+  %inc.lcssa = phi i32 [ %inc, %for.inc13 ]
+  store i64 %dec.6.lcssa.lcssa, i64* @e, align 8
+  br label %for.end14
+
+for.end14:
+  ret void
+}
+
+; CHECK: - Number of insts removed
+