commit 58e9ee85fda5083e2eea987917e8eab6ba31fe5e
author Jakob Stoklund Olesen <stoklund@2pi.dk> Fri Feb 05 22:03:18 2010 +0000
committer Jakob Stoklund Olesen <stoklund@2pi.dk> Fri Feb 05 22:03:18 2010 +0000
tree 542d47cbb2c02e5971df3c80b71b290118bd7877
parent 00cb3fe786855ce6545234bc3430223eb9272206

Teach SimplifyCFG about magic pointer constants.

Weird code sometimes uses pointer constants other than null. This patch
teaches SimplifyCFG to build switch instructions in those cases.

Code like this:

void f(const char *x) {
  if (!x)
    puts("null");
  else if ((uintptr_t)x == 1)
    puts("one");
  else if (x == (char*)2 || x == (char*)3)
    puts("two");
  else if ((intptr_t)x == 4)
    puts("four");
  else
    puts(x);
}

Now becomes a switch:

define void @f(i8* %x) nounwind ssp {
entry:
  %magicptr23 = ptrtoint i8* %x to i64            ; <i64> [#uses=1]
  switch i64 %magicptr23, label %if.else16 [
    i64 0, label %if.then
    i64 1, label %if.then2
    i64 2, label %if.then9
    i64 3, label %if.then9
    i64 4, label %if.then14
  ]

Note that LLVM's own DenseMap uses magic pointers.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@95439 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SimplifyCFGPass.cpp

diff --git a/lib/Transforms/Scalar/SimplifyCFGPass.cpp b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
index 43447de..62f34a2 100644
--- a/lib/Transforms/Scalar/SimplifyCFGPass.cpp
+++ b/lib/Transforms/Scalar/SimplifyCFGPass.cpp
@@ -30,6 +30,7 @@
 #include "llvm/Attributes.h"
 #include "llvm/Support/CFG.h"
 #include "llvm/Pass.h"
+#include "llvm/Target/TargetData.h"
 #include "llvm/ADT/SmallVector.h"
 #include "llvm/ADT/SmallPtrSet.h"
 #include "llvm/ADT/Statistic.h"
@@ -261,7 +262,7 @@
 
 /// IterativeSimplifyCFG - Call SimplifyCFG on all the blocks in the function,
 /// iterating until no more changes are made.
-static bool IterativeSimplifyCFG(Function &F) {
+static bool IterativeSimplifyCFG(Function &F, const TargetData *TD) {
   bool Changed = false;
   bool LocalChange = true;
   while (LocalChange) {
@@ -271,7 +272,7 @@
     // if they are unneeded...
     //
     for (Function::iterator BBIt = ++F.begin(); BBIt != F.end(); ) {
-      if (SimplifyCFG(BBIt++)) {
+      if (SimplifyCFG(BBIt++, TD)) {
         LocalChange = true;
         ++NumSimpl;
       }
@@ -285,10 +286,11 @@
 // simplify the CFG.
 //
 bool CFGSimplifyPass::runOnFunction(Function &F) {
+  const TargetData *TD = getAnalysisIfAvailable<TargetData>();
   bool EverChanged = RemoveUnreachableBlocksFromFn(F);
   EverChanged |= MergeEmptyReturnBlocks(F);
-  EverChanged |= IterativeSimplifyCFG(F);
-  
+  EverChanged |= IterativeSimplifyCFG(F, TD);
+
   // If neither pass changed anything, we're done.
   if (!EverChanged) return false;
 
@@ -299,11 +301,11 @@
   // RemoveUnreachableBlocksFromFn doesn't do anything.
   if (!RemoveUnreachableBlocksFromFn(F))
     return true;
-  
+
   do {
-    EverChanged = IterativeSimplifyCFG(F);
+    EverChanged = IterativeSimplifyCFG(F, TD);
     EverChanged |= RemoveUnreachableBlocksFromFn(F);
   } while (EverChanged);
-  
+
   return true;
 }