+
+gcc generates smaller code for this function at -O2 or -Os:
+
+void foo(signed char* p) {
+ if (*p == 3)
+ bar();
+ else if (*p == 4)
+ baz();
+ else if (*p == 5)
+ quux();
+}
+
+llvm decides it's a good idea to turn the repeated if...else into a
+binary tree, as if it were a switch; the resulting code requires -1
+compare-and-branches when *p<=2 or *p==5, the same number if *p==4
+or *p>6, and +1 if *p==3. So it should be a speed win
+(on balance). However, the revised code is larger, with 4 conditional
+branches instead of 3.
+
+More seriously, there is a byte->word extend before
+each comparison, where there should be only one, and the condition codes
+are not remembered when the same two values are compared twice.
+
+//===---------------------------------------------------------------------===//
+
+More register scavenging work:
+
+1. Use the register scavenger to track frame index materialized into registers
+ (those that do not fit in addressing modes) to allow reuse in the same BB.
+2. Finish scavenging for Thumb.
+
+//===---------------------------------------------------------------------===//
+
+More LSR enhancements possible:
+
+1. Teach LSR about pre- and post- indexed ops to allow iv increment be merged
+ in a load / store.
+2. Allow iv reuse even when a type conversion is required. For example, i8
+ and i32 load / store addressing modes are identical.
+
+
+//===---------------------------------------------------------------------===//
+
+This:
+
+int foo(int a, int b, int c, int d) {
+ long long acc = (long long)a * (long long)b;
+ acc += (long long)c * (long long)d;
+ return (int)(acc >> 32);
+}
+
+Should compile to use SMLAL (Signed Multiply Accumulate Long) which multiplies
+two signed 32-bit values to produce a 64-bit value, and accumulates this with
+a 64-bit value.
+
+We currently get this with both v4 and v6:
+
+_foo:
+ smull r1, r0, r1, r0
+ smull r3, r2, r3, r2
+ adds r3, r3, r1
+ adc r0, r2, r0
+ bx lr
+
+//===---------------------------------------------------------------------===//
+
+This:
+ #include <algorithm>
+ std::pair<unsigned, bool> full_add(unsigned a, unsigned b)
+ { return std::make_pair(a + b, a + b < a); }
+ bool no_overflow(unsigned a, unsigned b)
+ { return !full_add(a, b).second; }
+
+Should compile to:
+
+_Z8full_addjj:
+ adds r2, r1, r2
+ movcc r1, #0
+ movcs r1, #1
+ str r2, [r0, #0]
+ strb r1, [r0, #4]
+ mov pc, lr
+
+_Z11no_overflowjj:
+ cmn r0, r1
+ movcs r0, #0
+ movcc r0, #1
+ mov pc, lr
+
+not:
+
+__Z8full_addjj:
+ add r3, r2, r1
+ str r3, [r0]
+ mov r2, #1
+ mov r12, #0
+ cmp r3, r1
+ movlo r12, r2
+ str r12, [r0, #+4]
+ bx lr
+__Z11no_overflowjj:
+ add r3, r1, r0
+ mov r2, #1
+ mov r1, #0
+ cmp r3, r0
+ movhs r1, r2
+ mov r0, r1
+ bx lr
+
+//===---------------------------------------------------------------------===//
+
+Some of the NEON intrinsics may be appropriate for more general use, either
+as target-independent intrinsics or perhaps elsewhere in the ARM backend.
+Some of them may also be lowered to target-independent SDNodes, and perhaps
+some new SDNodes could be added.
+
+For example, maximum, minimum, and absolute value operations are well-defined
+and standard operations, both for vector and scalar types.
+
+The current NEON-specific intrinsics for count leading zeros and count one
+bits could perhaps be replaced by the target-independent ctlz and ctpop
+intrinsics. It may also make sense to add a target-independent "ctls"
+intrinsic for "count leading sign bits". Likewise, the backend could use
+the target-independent SDNodes for these operations.
+
+ARMv6 has scalar saturating and halving adds and subtracts. The same
+intrinsics could possibly be used for both NEON's vector implementations of
+those operations and the ARMv6 scalar versions.
+
+//===---------------------------------------------------------------------===//
+
+ARM::MOVCCr is commutable (by flipping the condition). But we need to implement
+ARMInstrInfo::commuteInstruction() to support it.
+
+//===---------------------------------------------------------------------===//
+
+Split out LDR (literal) from normal ARM LDR instruction. Also consider spliting
+LDR into imm12 and so_reg forms. This allows us to clean up some code. e.g.
+ARMLoadStoreOptimizer does not need to look at LDR (literal) and LDR (so_reg)
+while ARMConstantIslandPass only need to worry about LDR (literal).
+
+//===---------------------------------------------------------------------===//
+
+We need to fix constant isel for ARMv6t2 to use MOVT.
+
+//===---------------------------------------------------------------------===//
+
+Constant island pass should make use of full range SoImm values for LEApcrel.
+Be careful though as the last attempt caused infinite looping on lencod.
+
+//===---------------------------------------------------------------------===//
+
+Predication issue. This function:
+
+extern unsigned array[ 128 ];
+int foo( int x ) {
+ int y;
+ y = array[ x & 127 ];
+ if ( x & 128 )
+ y = 123456789 & ( y >> 2 );
+ else
+ y = 123456789 & y;
+ return y;
+}
+
+compiles to:
+
+_foo:
+ and r1, r0, #127
+ ldr r2, LCPI1_0
+ ldr r2, [r2]
+ ldr r1, [r2, +r1, lsl #2]
+ mov r2, r1, lsr #2
+ tst r0, #128
+ moveq r2, r1
+ ldr r0, LCPI1_1
+ and r0, r2, r0
+ bx lr
+
+It would be better to do something like this, to fold the shift into the
+conditional move:
+
+ and r1, r0, #127
+ ldr r2, LCPI1_0
+ ldr r2, [r2]
+ ldr r1, [r2, +r1, lsl #2]
+ tst r0, #128
+ movne r1, r1, lsr #2
+ ldr r0, LCPI1_1
+ and r0, r1, r0
+ bx lr
+
+it saves an instruction and a register.
+
+//===---------------------------------------------------------------------===//
+
+add/sub/and/or + i32 imm can be simplified by folding part of the immediate
+into the operation.
+
+//===---------------------------------------------------------------------===//
+
+It might be profitable to cse MOVi16 if there are lots of 32-bit immediates
+with the same bottom half.