From 6f819bd488d29bec2e60a4fff25d848f46ba36fb Mon Sep 17 00:00:00 2001
From: James Molloy <james.molloy@arm.com>
Date: Thu, 8 Oct 2015 12:39:59 +0000
Subject: [PATCH] Treat Mul just like Add and Subtract

Like adds and subtracts, muls ripple only to the left so we can use
the same logic.

While we're here, add a print method to DemandedBits so it can be used
with -analyze, which we'll use in the testcase.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@249686 91177308-0d34-0410-b5e6-96231b3b80d8
---
 include/llvm/Analysis/DemandedBits.h |  3 ++-
 lib/Analysis/DemandedBits.cpp        | 12 ++++++++++++
 test/Analysis/DemandedBits/basic.ll  | 12 ++++++++++++
 3 files changed, 26 insertions(+), 1 deletion(-)
 create mode 100644 test/Analysis/DemandedBits/basic.ll

diff --git a/include/llvm/Analysis/DemandedBits.h b/include/llvm/Analysis/DemandedBits.h
index d7562a5585c..42932bfd349 100644
--- a/include/llvm/Analysis/DemandedBits.h
+++ b/include/llvm/Analysis/DemandedBits.h
@@ -41,7 +41,8 @@ struct DemandedBits : public FunctionPass {
 
   bool runOnFunction(Function& F) override;
   void getAnalysisUsage(AnalysisUsage& AU) const override;
-
+  void print(raw_ostream &OS, const Module *M) const override;
+  
   /// Return the bits demanded from instruction I.
   APInt getDemandedBits(Instruction *I);
 
diff --git a/lib/Analysis/DemandedBits.cpp b/lib/Analysis/DemandedBits.cpp
index 775cbac4c53..6f92ba6289a 100644
--- a/lib/Analysis/DemandedBits.cpp
+++ b/lib/Analysis/DemandedBits.cpp
@@ -25,6 +25,7 @@
 #include "llvm/ADT/DepthFirstIterator.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/SmallVector.h"
+#include "llvm/ADT/StringExtras.h"
 #include "llvm/Analysis/AssumptionCache.h"
 #include "llvm/Analysis/ValueTracking.h"
 #include "llvm/IR/BasicBlock.h"
@@ -131,6 +132,7 @@ void DemandedBits::determineLiveOperandBits(
     break;
   case Instruction::Add:
   case Instruction::Sub:
+  case Instruction::Mul:
     // Find the highest live output bit. We don't need any more input
     // bits than that (adds, and thus subtracts, ripple only to the
     // left).
@@ -368,6 +370,16 @@ bool DemandedBits::isInstructionDead(Instruction *I) {
     !isAlwaysLive(I);
 }
 
+void DemandedBits::print(raw_ostream &OS, const Module *M) const {
+  // This is gross. But the alternative is making all the state mutable
+  // just because of this one debugging method.
+  const_cast<DemandedBits*>(this)->performAnalysis();
+  for (auto &KV : AliveBits) {
+    OS << "DemandedBits: 0x" << utohexstr(KV.second.getLimitedValue()) << " for "
+       << *KV.first << "\n";
+  }
+}
+
 FunctionPass *llvm::createDemandedBitsPass() {
   return new DemandedBits();
 }
diff --git a/test/Analysis/DemandedBits/basic.ll b/test/Analysis/DemandedBits/basic.ll
new file mode 100644
index 00000000000..3fd1b321288
--- /dev/null
+++ b/test/Analysis/DemandedBits/basic.ll
@@ -0,0 +1,12 @@
+; RUN: opt -S -demanded-bits -analyze < %s | FileCheck %s
+
+; CHECK-LABEL: 'test_mul'
+; CHECK-DAG: DemandedBits: 0xFF for   %1 = add nsw i32 %a, 5
+; CHECK-DAG: DemandedBits: 0xFF for   %3 = trunc i32 %2 to i8
+; CHECK-DAG: DemandedBits: 0xFF for   %2 = mul nsw i32 %1, %b
+define i8 @test_mul(i32 %a, i32 %b) {
+  %1 = add nsw i32 %a, 5
+  %2 = mul nsw i32 %1, %b
+  %3 = trunc i32 %2 to i8
+  ret i8 %3
+}
-- 
2.34.1