From db059db6ad199a4188d6a5ce3e7812e291afeb6e Mon Sep 17 00:00:00 2001
From: Tim Northover <tnorthover@apple.com>
Date: Tue, 28 Jul 2015 22:42:32 +0000
Subject: [PATCH] AArch64: be careful of large immediates when optimising cmps.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@243492 91177308-0d34-0410-b5e6-96231b3b80d8
---
 .../AArch64/AArch64ConditionOptimizer.cpp     | 17 ++++++++----
 .../AArch64/combine-comparisons-by-cse.ll     | 26 +++++++++++++++++++
 2 files changed, 38 insertions(+), 5 deletions(-)

diff --git a/lib/Target/AArch64/AArch64ConditionOptimizer.cpp b/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
index b9e41c61def..99a5eaa7aef 100644
--- a/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
+++ b/lib/Target/AArch64/AArch64ConditionOptimizer.cpp
@@ -154,11 +154,18 @@ MachineInstr *AArch64ConditionOptimizer::findSuitableCompare(
     // cmn is an alias for adds with a dead destination register.
     case AArch64::ADDSWri:
     case AArch64::ADDSXri:
-      if (MRI->use_empty(I->getOperand(0).getReg()))
-        return I;
-
-      DEBUG(dbgs() << "Destination of cmp is not dead, " << *I << '\n');
-      return nullptr;
+      if (!I->getOperand(2).isImm()) {
+        DEBUG(dbgs() << "Immediate of cmp is symbolic, " << *I << '\n');
+        return nullptr;
+      } else if (I->getOperand(2).getImm() << I->getOperand(3).getImm() >=
+                 0xfff) {
+        DEBUG(dbgs() << "Immediate of cmp may be out of range, " << *I << '\n');
+        return nullptr;
+      } else if (!MRI->use_empty(I->getOperand(0).getReg())) {
+        DEBUG(dbgs() << "Destination of cmp is not dead, " << *I << '\n');
+        return nullptr;
+      }
+      return I;
 
     // Prevent false positive case like:
     // cmp      w19, #0
diff --git a/test/CodeGen/AArch64/combine-comparisons-by-cse.ll b/test/CodeGen/AArch64/combine-comparisons-by-cse.ll
index c78fabac618..004267f4e4e 100644
--- a/test/CodeGen/AArch64/combine-comparisons-by-cse.ll
+++ b/test/CodeGen/AArch64/combine-comparisons-by-cse.ll
@@ -403,6 +403,32 @@ return:                                           ; preds = %land.lhs.true, %con
   ret i32 %retval.0
 }
 
+define void @cmp_shifted(i32 %in, i32 %lhs, i32 %rhs) {
+; CHECK-LABEL: cmp_shifted:
+; CHECK: cmp w0, #1
+; [...]
+; CHECK: cmp w0, #2, lsl #12
+
+  %tst_low = icmp sgt i32 %in, 0
+  br i1 %tst_low, label %true, label %false
+
+true:
+  call i32 @zoo(i32 128)
+  ret void
+
+false:
+  %tst = icmp sgt i32 %in, 8191
+  br i1 %tst, label %truer, label %falser
+
+truer:
+  call i32 @zoo(i32 42)
+  ret void
+
+falser:
+  call i32 @zoo(i32 1)
+  ret void
+}
+
 declare i32 @zoo(i32)
 
 declare double @yoo(i32)