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58e9ee85fd
llvm-6502/lib/Transforms
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Jakob Stoklund Olesen 58e9ee85fd 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
2010-02-05 22:03:18 +00:00
..
Hello make -fno-rtti the default unless a directory builds with REQUIRES_RTTI. 2010-01-24 20:43:08 +00:00
InstCombine fix logical-select to invoke filecheck right, and fix hte instcombine 2010-02-05 19:53:02 +00:00
Instrumentation make -fno-rtti the default unless a directory builds with REQUIRES_RTTI. 2010-01-24 20:43:08 +00:00
IPO Increase inliner thresholds by 25. 2010-02-04 18:48:20 +00:00
Scalar Teach SimplifyCFG about magic pointer constants. 2010-02-05 22:03:18 +00:00
Utils Teach SimplifyCFG about magic pointer constants. 2010-02-05 22:03:18 +00:00
Makefile move instcombine to its own library, it's past time. 2010-01-04 06:23:24 +00:00