Allocate local registers in order for optimal coloring.

Also avoid locals evicting locals just because they want a cheaper register.

Problem: MI Sched knows exactly how many registers we have and assumes
they can be colored. In cases where we have large blocks, usually from
unrolled loops, greedy coloring fails. This is a source of
"regressions" from the MI Scheduler on x86. I noticed this issue on
x86 where we have long chains of two-address defs in the same live
range. It's easy to see this in matrix multiplication benchmarks like
IRSmk and even the unit test misched-matmul.ll.

A fundamental difference between the LLVM register allocator and
conventional graph coloring is that in our model a live range can't
discover its neighbors, it can only verify its neighbors. That's why
we initially went for greedy coloring and added eviction to deal with
the hard cases. However, for singly defined and two-address live
ranges, we can optimally color without visiting neighbors simply by
processing the live ranges in instruction order.

Other beneficial side effects:

It is much easier to understand and debug regalloc for large blocks
when the live ranges are allocated in order. Yes, global allocation is
still very confusing, but it's nice to be able to comprehend what
happened locally.

Heuristics could be added to bias register assignment based on
instruction locality (think late register pairing, banks...).

Intuituvely this will make some test cases that are on the threshold
of register pressure more stable.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@187139 91177308-0d34-0410-b5e6-96231b3b80d8

1 files changed, 18 insertions, 18 deletions

diff --git a/test/CodeGen/X86/sse3.ll b/test/CodeGen/X86/sse3.ll
index 4c95c9fb75..6d5b19243e 100644
--- a/test/CodeGen/X86/sse3.ll
+++ b/test/CodeGen/X86/sse3.ll
@@ -14,7 +14,7 @@ entry:
                 <8 x i32> < i32 8, i32 0, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef, i32 undef  >
 	store <8 x i16> %tmp6, <8 x i16>* %dest
 	ret void
-        
+
 ; X64-LABEL: t0:
 ; X64:	movdqa	(%rsi), %xmm0
 ; X64:	pslldq	$2, %xmm0
@@ -27,7 +27,7 @@ define <8 x i16> @t1(<8 x i16>* %A, <8 x i16>* %B) nounwind {
 	%tmp2 = load <8 x i16>* %B
 	%tmp3 = shufflevector <8 x i16> %tmp1, <8 x i16> %tmp2, <8 x i32> < i32 8, i32 1, i32 2, i32 3, i32 4, i32 5, i32 6, i32 7 >
 	ret <8 x i16> %tmp3
-        
+
 ; X64-LABEL: t1:
 ; X64: 	movdqa	(%rdi), %xmm0
 ; X64: 	pinsrw	$0, (%rsi), %xmm0
@@ -63,7 +63,7 @@ define <8 x i16> @t4(<8 x i16> %A, <8 x i16> %B) nounwind {
 ; X64: 	pshufhw	$100, [[XMM0]], [[XMM1:%xmm[0-9]+]]
 ; X64: 	pinsrw	$1, %eax, [[XMM1]]
 ; X64: 	pextrw	$1, [[XMM0]], %eax
-; X64: 	pinsrw	$4, %eax, %xmm0
+; X64: 	pinsrw	$4, %eax, %xmm{{[0-9]}}
 ; X64: 	ret
 }
 
@@ -127,13 +127,13 @@ define void @t9(<4 x float>* %r, <2 x i32>* %A) nounwind {
 	%tmp.upgrd.3 = bitcast <2 x i32>* %A to double*
 	%tmp.upgrd.4 = load double* %tmp.upgrd.3
 	%tmp.upgrd.5 = insertelement <2 x double> undef, double %tmp.upgrd.4, i32 0
-	%tmp5 = insertelement <2 x double> %tmp.upgrd.5, double undef, i32 1	
-	%tmp6 = bitcast <2 x double> %tmp5 to <4 x float>	
-	%tmp.upgrd.6 = extractelement <4 x float> %tmp, i32 0	
-	%tmp7 = extractelement <4 x float> %tmp, i32 1		
-	%tmp8 = extractelement <4 x float> %tmp6, i32 0		
-	%tmp9 = extractelement <4 x float> %tmp6, i32 1		
-	%tmp10 = insertelement <4 x float> undef, float %tmp.upgrd.6, i32 0	
+	%tmp5 = insertelement <2 x double> %tmp.upgrd.5, double undef, i32 1
+	%tmp6 = bitcast <2 x double> %tmp5 to <4 x float>
+	%tmp.upgrd.6 = extractelement <4 x float> %tmp, i32 0
+	%tmp7 = extractelement <4 x float> %tmp, i32 1
+	%tmp8 = extractelement <4 x float> %tmp6, i32 0
+	%tmp9 = extractelement <4 x float> %tmp6, i32 1
+	%tmp10 = insertelement <4 x float> undef, float %tmp.upgrd.6, i32 0
 	%tmp11 = insertelement <4 x float> %tmp10, float %tmp7, i32 1
 	%tmp12 = insertelement <4 x float> %tmp11, float %tmp8, i32 2
 	%tmp13 = insertelement <4 x float> %tmp12, float %tmp9, i32 3
@@ -155,21 +155,21 @@ define void @t9(<4 x float>* %r, <2 x i32>* %A) nounwind {
 @g2 = external constant <4 x i16>
 
 define internal void @t10() nounwind {
-        load <4 x i32>* @g1, align 16 
+        load <4 x i32>* @g1, align 16
         bitcast <4 x i32> %1 to <8 x i16>
         shufflevector <8 x i16> %2, <8 x i16> undef, <8 x i32> < i32 0, i32 2, i32 4, i32 6, i32 undef, i32 undef, i32 undef, i32 undef >
-        bitcast <8 x i16> %3 to <2 x i64>  
-        extractelement <2 x i64> %4, i32 0 
-        bitcast i64 %5 to <4 x i16>        
+        bitcast <8 x i16> %3 to <2 x i64>
+        extractelement <2 x i64> %4, i32 0
+        bitcast i64 %5 to <4 x i16>
         store <4 x i16> %6, <4 x i16>* @g2, align 8
         ret void
 ; X64: 	t10:
-; X64: 		pextrw	$4, [[X0:%xmm[0-9]+]], %ecx
-; X64: 		pextrw	$6, [[X0]], %eax
+; X64: 		pextrw	$4, [[X0:%xmm[0-9]+]], %e{{..}}
+; X64: 		pextrw	$6, [[X0]], %e{{..}}
 ; X64: 		movlhps [[X0]], [[X0]]
 ; X64: 		pshuflw	$8, [[X0]], [[X0]]
-; X64: 		pinsrw	$2, %ecx, [[X0]]
-; X64: 		pinsrw	$3, %eax, [[X0]]
+; X64: 		pinsrw	$2, %e{{..}}, [[X0]]
+; X64: 		pinsrw	$3, %e{{..}}, [[X0]]
 }