Moving potential optimizations out of PR2330 into lib/Target/README.txt.

Hopefully this isn't too much stuff to dump into this file.



git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@60285 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 262 insertions, 0 deletions

diff --git a/lib/Target/README.txt b/lib/Target/README.txt
index dfc7e51afd..b0d93f0264 100644
--- a/lib/Target/README.txt
+++ b/lib/Target/README.txt
@@ -1002,3 +1002,265 @@ define i8 @addshr(i8 %x) readnone nounwind {
 }
 
 //===---------------------------------------------------------------------===//
+
+From gcc bug 24696:
+int
+f (unsigned long a, unsigned long b, unsigned long c)
+{
+  return ((a & (c - 1)) != 0) || ((b & (c - 1)) != 0);
+}
+int
+f (unsigned long a, unsigned long b, unsigned long c)
+{
+  return ((a & (c - 1)) != 0) | ((b & (c - 1)) != 0);
+}
+Both should combine to ((a|b) & (c-1)) != 0.  Currently not optimized with
+"clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 20192:
+#define PMD_MASK    (~((1UL << 23) - 1))
+void clear_pmd_range(unsigned long start, unsigned long end)
+{
+   if (!(start & ~PMD_MASK) && !(end & ~PMD_MASK))
+       f();
+}
+The expression should optimize to something like
+"!((start|end)&~PMD_MASK). Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 15241:
+unsigned int
+foo (unsigned int a, unsigned int b)
+{
+ if (a <= 7 && b <= 7)
+   baz ();
+}
+Should combine to "(a|b) <= 7".  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 3756:
+int
+pn (int n)
+{
+ return (n >= 0 ? 1 : -1);
+}
+Should combine to (n >> 31) | 1.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts | llc".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 28685:
+int test(int a, int b)
+{
+ int lt = a < b;
+ int eq = a == b;
+
+ return (lt || eq);
+}
+Should combine to "a <= b".  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts | llc".
+
+//===---------------------------------------------------------------------===//
+
+void a(int variable)
+{
+ if (variable == 4 || variable == 6)
+   bar();
+}
+This should optimize to "if ((variable | 2) == 6)".  Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts | llc".
+
+//===---------------------------------------------------------------------===//
+
+unsigned int f(unsigned int i, unsigned int n) {++i; if (i == n) ++i; return
+i;}
+unsigned int f2(unsigned int i, unsigned int n) {++i; i += i == n; return i;}
+These should combine to the same thing.  Currently, the first function
+produces better code on X86.
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 33512:
+int f(int y, int x)
+{
+ return x & ((~x) | y);
+}
+Should combine to x & y.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 15784:
+#define abs(x) x>0?x:-x
+int f(int x, int y)
+{
+ return (abs(x)) >= 0;
+}
+This should optimize to x == INT_MIN. (With -fwrapv.)  Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 14753:
+void
+rotate_cst (unsigned int a)
+{
+ a = (a << 10) | (a >> 22);
+ if (a == 123)
+   bar ();
+}
+void
+minus_cst (unsigned int a)
+{
+ unsigned int tem;
+
+ tem = 20 - a;
+ if (tem == 5)
+   bar ();
+}
+void
+mask_gt (unsigned int a)
+{
+ /* This is equivalent to a > 15.  */
+ if ((a & ~7) > 8)
+   bar ();
+}
+void
+rshift_gt (unsigned int a)
+{
+ /* This is equivalent to a > 23.  */
+ if ((a >> 2) > 5)
+   bar ();
+}
+All should simplify to a single comparison.  All of these are
+currently not optimized with "clang -emit-llvm-bc | opt
+-std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+From GCC Bug 32605:
+int c(int* x) {return (char*)x+2 == (char*)x;}
+Should combine to 0.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts" (although llc can optimize it).
+
+//===---------------------------------------------------------------------===//
+
+int a(unsigned char* b) {return *b > 99;}
+There's an unnecessary zext in the generated code with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b) {return ((a|b)&1) | (b&-2);}
+Should be combined to "(a&1)|b".  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(unsigned b) {return ((b << 31) | (b << 30)) >> 31;}
+Should be combined to  "((b >> 1) | b) & 1".  Currently not optimized
+with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned x, unsigned y) { return x | (y & 1) | (y & 2);}
+Should combine to "x | (y & 3)".  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned a) {return ((a | 1) & 3) | (a & -4);}
+Should combine to "a | 1".  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return ((a&~b) | (~a&b));}
+Should fold to xor.  Currently not optimized with "clang -emit-llvm-bc
+| opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return (~a & c) | ((c|a) & b);}
+Should fold to "(~a & c) | (a & b)".  Currently not optimized with
+"clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a,int b) {return (~(a|b))|a;}
+Should fold to "a|~b".  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b) {return (a&&b) || (a&&!b);}
+Should fold to "a".  Currently not optimized with "clang -emit-llvm-bc
+| opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return (a&&b) || (!a&&c);}
+Should fold to "a ? b : c", or at least something sane.  Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int a, int b, int c) {return (a&&b) || (a&&c) || (a&&b&&c);}
+Should fold to a && (b || c).  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return x | ((x & 8) ^ 8);}
+Should combine to x | 8.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return x ^ ((x & 8) ^ 8);}
+Should also combine to x | 8.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return (x & 8) == 0 ? -1 : -9;}
+Should combine to (x | -9) ^ 8.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return (x & 8) == 0 ? -9 : -1;}
+Should combine to x | -9.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+int a(int x) {return ((x | -9) ^ 8) & x;}
+Should combine to x & -9.  Currently not optimized with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned a) {return a * 0x11111111 >> 28 & 1;}
+Should combine to "a * 0x88888888 >> 31".  Currently not optimized
+with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(char* x) {if ((*x & 32) == 0) return b();}
+There's an unnecessary zext in the generated code with "clang
+-emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//
+
+unsigned a(unsigned long long x) {return 40 * (x >> 1);}
+Should combine to "20 * (((unsigned)x) & -2)".  Currently not
+optimized with "clang -emit-llvm-bc | opt -std-compile-opts".
+
+//===---------------------------------------------------------------------===//