From: Dan Gohman <gohman@apple.com>
Date: Tue, 13 Jan 2009 23:23:30 +0000 (+0000)
Subject: Disable the register+memory forms of the bt instructions for now. Thanks
X-Git-Url: http://demsky.eecs.uci.edu/git/?a=commitdiff_plain;h=f31408d75c42f48041e40aaaee147dcaa8477bc0;p=oota-llvm.git

Disable the register+memory forms of the bt instructions for now. Thanks
to Eli for pointing out that these forms don't ignore the high bits of
their index operands, and as such are not immediately suitable for use
by isel.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@62194 91177308-0d34-0410-b5e6-96231b3b80d8
---

diff --git a/lib/Target/X86/X86Instr64bit.td b/lib/Target/X86/X86Instr64bit.td
index bcf1ebdeace..857fbf86b29 100644
--- a/lib/Target/X86/X86Instr64bit.td
+++ b/lib/Target/X86/X86Instr64bit.td
@@ -924,10 +924,14 @@ def BT64rr : RI<0xA3, MRMDestReg, (outs), (ins GR64:$src1, GR64:$src2),
                "bt{q}\t{$src2, $src1|$src1, $src2}",
                [(X86bt GR64:$src1, GR64:$src2),
                 (implicit EFLAGS)]>, TB;
-def BT64mr : RI<0xA3, MRMDestMem, (outs), (ins i64mem:$src1, GR64:$src2),
-               "bt{q}\t{$src2, $src1|$src1, $src2}",
-               [(X86bt (loadi64 addr:$src1), GR64:$src2),
-                (implicit EFLAGS)]>, TB;
+
+// Unlike with the register+register form, the memory+register form of the
+// bt instruction does not ignore the high bits of the index. From ISel's
+// perspective, this is pretty bizarre. Disable these instructions for now.
+//def BT64mr : RI<0xA3, MRMDestMem, (outs), (ins i64mem:$src1, GR64:$src2),
+//               "bt{q}\t{$src2, $src1|$src1, $src2}",
+//               [(X86bt (loadi64 addr:$src1), GR64:$src2),
+//                (implicit EFLAGS)]>, TB;
 
 def BT64ri8 : Ii8<0xBA, MRM4r, (outs), (ins GR64:$src1, i64i8imm:$src2),
                 "bt{q}\t{$src2, $src1|$src1, $src2}",
diff --git a/lib/Target/X86/X86InstrInfo.td b/lib/Target/X86/X86InstrInfo.td
index 0eaab8d93d1..73aa15a81d7 100644
--- a/lib/Target/X86/X86InstrInfo.td
+++ b/lib/Target/X86/X86InstrInfo.td
@@ -2682,14 +2682,18 @@ def BT32rr : I<0xA3, MRMDestReg, (outs), (ins GR32:$src1, GR32:$src2),
                "bt{l}\t{$src2, $src1|$src1, $src2}",
                [(X86bt GR32:$src1, GR32:$src2),
                 (implicit EFLAGS)]>, TB;
-def BT16mr : I<0xA3, MRMDestMem, (outs), (ins i16mem:$src1, GR16:$src2),
-               "bt{w}\t{$src2, $src1|$src1, $src2}",
-               [(X86bt (loadi16 addr:$src1), GR16:$src2),
-                (implicit EFLAGS)]>, OpSize, TB, Requires<[FastBTMem]>;
-def BT32mr : I<0xA3, MRMDestMem, (outs), (ins i32mem:$src1, GR32:$src2),
-               "bt{l}\t{$src2, $src1|$src1, $src2}",
-               [(X86bt (loadi32 addr:$src1), GR32:$src2),
-                (implicit EFLAGS)]>, TB, Requires<[FastBTMem]>;
+
+// Unlike with the register+register form, the memory+register form of the
+// bt instruction does not ignore the high bits of the index. From ISel's
+// perspective, this is pretty bizarre. Disable these instructions for now.
+//def BT16mr : I<0xA3, MRMDestMem, (outs), (ins i16mem:$src1, GR16:$src2),
+//               "bt{w}\t{$src2, $src1|$src1, $src2}",
+//               [(X86bt (loadi16 addr:$src1), GR16:$src2),
+//                (implicit EFLAGS)]>, OpSize, TB, Requires<[FastBTMem]>;
+//def BT32mr : I<0xA3, MRMDestMem, (outs), (ins i32mem:$src1, GR32:$src2),
+//               "bt{l}\t{$src2, $src1|$src1, $src2}",
+//               [(X86bt (loadi32 addr:$src1), GR32:$src2),
+//                (implicit EFLAGS)]>, TB, Requires<[FastBTMem]>;
 
 def BT16ri8 : Ii8<0xBA, MRM4r, (outs), (ins GR16:$src1, i16i8imm:$src2),
                 "bt{w}\t{$src2, $src1|$src1, $src2}",
diff --git a/test/CodeGen/X86/bt.ll b/test/CodeGen/X86/bt.ll
index b63a3f8ecf7..86254d3295b 100644
--- a/test/CodeGen/X86/bt.ll
+++ b/test/CodeGen/X86/bt.ll
@@ -1,7 +1,12 @@
 ; RUN: llvm-as < %s | llc | grep btl
-; RUN: llvm-as < %s | llc -mcpu=pentium4 | grep btl | grep esp
+; RUN: llvm-as < %s | llc -mcpu=pentium4 | grep btl | not grep esp
 ; RUN: llvm-as < %s | llc -mcpu=penryn   | grep btl | not grep esp
 ; PR3253
+
+; The register+memory form of the BT instruction should be usable on
+; pentium4, however it is currently disabled due to the register+memory
+; form having different semantics than the register+register form.
+
 target datalayout = "e-p:32:32:32-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:32:64-f32:32:32-f64:32:64-v64:64:64-v128:128:128-a0:0:64-f80:128:128"
 target triple = "i386-apple-darwin8"