+
+//===---------------------------------------------------------------------===//
+rdar://5907648
+
+This function:
+
+float foo(unsigned char x) {
+ return x;
+}
+
+compiles to (x86-32):
+
+define float @foo(i8 zeroext %x) nounwind {
+ %tmp12 = uitofp i8 %x to float ; <float> [#uses=1]
+ ret float %tmp12
+}
+
+compiles to:
+
+_foo:
+ subl $4, %esp
+ movzbl 8(%esp), %eax
+ cvtsi2ss %eax, %xmm0
+ movss %xmm0, (%esp)
+ flds (%esp)
+ addl $4, %esp
+ ret
+
+We should be able to use:
+ cvtsi2ss 8($esp), %xmm0
+since we know the stack slot is already zext'd.
+
+//===---------------------------------------------------------------------===//
+
+Consider using movlps instead of movsd to implement (scalar_to_vector (loadf64))
+when code size is critical. movlps is slower than movsd on core2 but it's one
+byte shorter.
+
+//===---------------------------------------------------------------------===//
+
+We should use a dynamic programming based approach to tell when using FPStack
+operations is cheaper than SSE. SciMark montecarlo contains code like this
+for example:
+
+double MonteCarlo_num_flops(int Num_samples) {
+ return ((double) Num_samples)* 4.0;
+}
+
+In fpstack mode, this compiles into:
+
+LCPI1_0:
+ .long 1082130432 ## float 4.000000e+00
+_MonteCarlo_num_flops:
+ subl $4, %esp
+ movl 8(%esp), %eax
+ movl %eax, (%esp)
+ fildl (%esp)
+ fmuls LCPI1_0
+ addl $4, %esp
+ ret
+
+in SSE mode, it compiles into significantly slower code:
+
+_MonteCarlo_num_flops:
+ subl $12, %esp
+ cvtsi2sd 16(%esp), %xmm0
+ mulsd LCPI1_0, %xmm0
+ movsd %xmm0, (%esp)
+ fldl (%esp)
+ addl $12, %esp
+ ret
+
+There are also other cases in scimark where using fpstack is better, it is
+cheaper to do fld1 than load from a constant pool for example, so
+"load, add 1.0, store" is better done in the fp stack, etc.
+
+//===---------------------------------------------------------------------===//
+
+The X86 backend should be able to if-convert SSE comparisons like "ucomisd" to
+"cmpsd". For example, this code:
+
+double d1(double x) { return x == x ? x : x + x; }
+
+Compiles into:
+
+_d1:
+ ucomisd %xmm0, %xmm0
+ jnp LBB1_2
+ addsd %xmm0, %xmm0
+ ret
+LBB1_2:
+ ret
+
+Also, the 'ret's should be shared. This is PR6032.
+
+//===---------------------------------------------------------------------===//
+
+These should compile into the same code (PR6214): Perhaps instcombine should
+canonicalize the former into the later?
+
+define float @foo(float %x) nounwind {
+ %t = bitcast float %x to i32
+ %s = and i32 %t, 2147483647
+ %d = bitcast i32 %s to float
+ ret float %d
+}
+
+declare float @fabsf(float %n)
+define float @bar(float %x) nounwind {
+ %d = call float @fabsf(float %x)
+ ret float %d
+}
+
+//===---------------------------------------------------------------------===//
+
+This IR (from PR6194):
+
+target datalayout = "e-p:64:64:64-i1:8:8-i8:8:8-i16:16:16-i32:32:32-i64:64:64-f32:32:32-f64:64:64-v64:64:64-v128:128:128-a0:0:64-s0:64:64-f80:128:128-n8:16:32:64-S128"
+target triple = "x86_64-apple-darwin10.0.0"
+
+%0 = type { double, double }
+%struct.float3 = type { float, float, float }
+
+define void @test(%0, %struct.float3* nocapture %res) nounwind noinline ssp {
+entry:
+ %tmp18 = extractvalue %0 %0, 0 ; <double> [#uses=1]
+ %tmp19 = bitcast double %tmp18 to i64 ; <i64> [#uses=1]
+ %tmp20 = zext i64 %tmp19 to i128 ; <i128> [#uses=1]
+ %tmp10 = lshr i128 %tmp20, 32 ; <i128> [#uses=1]
+ %tmp11 = trunc i128 %tmp10 to i32 ; <i32> [#uses=1]
+ %tmp12 = bitcast i32 %tmp11 to float ; <float> [#uses=1]
+ %tmp5 = getelementptr inbounds %struct.float3* %res, i64 0, i32 1 ; <float*> [#uses=1]
+ store float %tmp12, float* %tmp5
+ ret void
+}
+
+Compiles to:
+
+_test: ## @test
+ movd %xmm0, %rax
+ shrq $32, %rax
+ movl %eax, 4(%rdi)
+ ret
+
+This would be better kept in the SSE unit by treating XMM0 as a 4xfloat and
+doing a shuffle from v[1] to v[0] then a float store.
+
+//===---------------------------------------------------------------------===//
+
+On SSE4 machines, we compile this code:
+
+define <2 x float> @test2(<2 x float> %Q, <2 x float> %R,
+ <2 x float> *%P) nounwind {
+ %Z = fadd <2 x float> %Q, %R
+
+ store <2 x float> %Z, <2 x float> *%P
+ ret <2 x float> %Z
+}
+
+into:
+
+_test2: ## @test2
+## BB#0:
+ insertps $0, %xmm2, %xmm2
+ insertps $16, %xmm3, %xmm2
+ insertps $0, %xmm0, %xmm3
+ insertps $16, %xmm1, %xmm3
+ addps %xmm2, %xmm3
+ movq %xmm3, (%rdi)
+ movaps %xmm3, %xmm0
+ pshufd $1, %xmm3, %xmm1
+ ## kill: XMM1<def> XMM1<kill>
+ ret
+
+The insertps's of $0 are pointless complex copies.
+
+//===---------------------------------------------------------------------===//
+
+[UNSAFE FP]
+
+void foo(double, double, double);
+void norm(double x, double y, double z) {
+ double scale = __builtin_sqrt(x*x + y*y + z*z);
+ foo(x/scale, y/scale, z/scale);
+}
+
+We currently generate an sqrtsd and 3 divsd instructions. This is bad, fp div is
+slow and not pipelined. In -ffast-math mode we could compute "1.0/scale" first
+and emit 3 mulsd in place of the divs. This can be done as a target-independent
+transform.
+
+If we're dealing with floats instead of doubles we could even replace the sqrtss
+and inversion with an rsqrtss instruction, which computes 1/sqrt faster at the
+cost of reduced accuracy.
+
+//===---------------------------------------------------------------------===//
+
+This function should be matched to haddpd when the appropriate CPU is enabled:
+
+#include <x86intrin.h>
+double f (__m128d p) {
+ return p[0] + p[1];
+}
+
+similarly, v[0]-v[1] should match to hsubpd, and {v[0]-v[1], w[0]-w[1]} should
+turn into hsubpd also.
+
+//===---------------------------------------------------------------------===//
+
+define <2 x i32> @foo(<2 x double> %in) {
+ %x = fptosi <2 x double> %in to <2 x i32>
+ ret <2 x i32> %x
+}
+
+Should compile into cvttpd2dq instead of being scalarized into 2 cvttsd2si.
+
+//===---------------------------------------------------------------------===//
projects / oota-llvm.git / blobdiff