Remove a fixed item, update a couple partially-fixed items.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@105375 91177308-0d34-0410-b5e6-96231b3b80d8

diff --git a/lib/Target/X86/README.txt b/lib/Target/X86/README.txt
index d4545a6fcfd37150820e69ae6bb268a45c2d7e4d..efc0cd82f23e991db73c83339a88b83661039c3a 100644 (file)
--- a/lib/Target/X86/README.txt
+++ b/lib/Target/X86/README.txt
@@ -1103,57 +1103,6 @@ be folded into: shl [mem], 1
 
 //===---------------------------------------------------------------------===//
 
-This testcase misses a read/modify/write opportunity (from PR1425):
-
-void vertical_decompose97iH1(int *b0, int *b1, int *b2, int width){
-    int i;
-    for(i=0; i<width; i++)
-        b1[i] += (1*(b0[i] + b2[i])+0)>>0;
-}
-
-We compile it down to:
-
-LBB1_2:        # bb
-       movl    (%esi,%edi,4), %ebx
-       addl    (%ecx,%edi,4), %ebx
-       addl    (%edx,%edi,4), %ebx
-       movl    %ebx, (%ecx,%edi,4)
-       incl    %edi
-       cmpl    %eax, %edi
-       jne     LBB1_2  # bb
-
-the inner loop should add to the memory location (%ecx,%edi,4), saving
-a mov.  Something like:
-
-        movl    (%esi,%edi,4), %ebx
-        addl    (%edx,%edi,4), %ebx
-        addl    %ebx, (%ecx,%edi,4)
-
-Here is another interesting example:
-
-void vertical_compose97iH1(int *b0, int *b1, int *b2, int width){
-    int i;
-    for(i=0; i<width; i++)
-        b1[i] -= (1*(b0[i] + b2[i])+0)>>0;
-}
-
-We miss the r/m/w opportunity here by using 2 subs instead of an add+sub[mem]:
-
-LBB9_2:        # bb
-       movl    (%ecx,%edi,4), %ebx
-       subl    (%esi,%edi,4), %ebx
-       subl    (%edx,%edi,4), %ebx
-       movl    %ebx, (%ecx,%edi,4)
-       incl    %edi
-       cmpl    %eax, %edi
-       jne     LBB9_2  # bb
-
-Additionally, LSR should rewrite the exit condition of these loops to use
-a stride-4 IV, would would allow all the scales in the loop to go away.
-This would result in smaller code and more efficient microops.
-
-//===---------------------------------------------------------------------===//
-
 In SSE mode, we turn abs and neg into a load from the constant pool plus a xor
 or and instruction, for example:
 
@@ -1301,15 +1250,8 @@ FirstOnet:
         xorl    %eax, %eax
         ret
 
-There are a few possible improvements here:
-1. We should be able to eliminate the dead load into %ecx
-2. We could change the "movl 8(%esp), %eax" into
-   "movzwl 10(%esp), %eax"; this lets us change the cmpl
-   into a testl, which is shorter, and eliminate the shift.
-
-We could also in theory eliminate the branch by using a conditional
-for the address of the load, but that seems unlikely to be worthwhile
-in general.
+We could change the "movl 8(%esp), %eax" into "movzwl 10(%esp), %eax"; this
+lets us change the cmpl into a testl, which is shorter, and eliminate the shift.
 
 //===---------------------------------------------------------------------===//
 
@@ -1331,22 +1273,23 @@ bb7:            ; preds = %entry
 
 to:
 
-_foo:
+foo:                                    # @foo
+# BB#0:                                 # %entry
+       movl    4(%esp), %ecx
        cmpb    $0, 16(%esp)
-       movl    12(%esp), %ecx
+       je      .LBB0_2
+# BB#1:                                 # %bb
        movl    8(%esp), %eax
-       movl    4(%esp), %edx
-       je      LBB1_2  # bb7
-LBB1_1:        # bb
-       addl    %edx, %eax
+       addl    %ecx, %eax
        ret
-LBB1_2:        # bb7
-       movl    %edx, %eax
-       subl    %ecx, %eax
+.LBB0_2:                                # %bb7
+       movl    12(%esp), %edx
+       movl    %ecx, %eax
+       subl    %edx, %eax
        ret
 
-The coalescer could coalesce "edx" with "eax" to avoid the movl in LBB1_2
-if it commuted the addl in LBB1_1.
+There's an obviously unnecessary movl in .LBB0_2, and we could eliminate a
+couple more movls by putting 4(%esp) into %eax instead of %ecx.
 
 //===---------------------------------------------------------------------===//
 
@@ -1396,8 +1339,7 @@ Also check why xmm7 is not used at all in the function.
 
 //===---------------------------------------------------------------------===//
 
-Legalize loses track of the fact that bools are always zero extended when in
-memory.  This causes us to compile abort_gzip (from 164.gzip) from:
+Take the following:
 
 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"
@@ -1416,16 +1358,15 @@ bb4.i:          ; preds = %entry
 }
 declare void @exit(i32) noreturn nounwind 
 
-into:
-
-_abort_gzip:
+This compiles into:
+_abort_gzip:                            ## @abort_gzip
+## BB#0:                                ## %entry
        subl    $12, %esp
        movb    _in_exit.4870.b, %al
-       notb    %al
-       testb   $1, %al
-       jne     LBB1_2  ## bb4.i
-LBB1_1:        ## bb.i
-  ...
+       cmpb    $1, %al
+       jne     LBB0_2
+
+We somehow miss folding the movb into the cmpb.
 
 //===---------------------------------------------------------------------===//